Tunable microwave-assisted method for the solvent-free and catalyst-free peracetylation of natural products

Article abstract of DOI:10.3762/bjoc.12.214

Background: The peracetylation is a simple chemical modification that can be used to enhance the bioavailability of hydrophilic products and to obtain safe and stable pro-drugs. Results: A totally green, solvent-free and catalyst-free microwave (MW)-assisted method for peracetylation of natural products such as oleuropein, alpha-hederin, quercetin and rutin is presented. By simply tuning the MW heating program, polyols with chemical diverse -OH groups or thermolabile functionalities can be peracetylated to improve the biological activity without degradation of the natural starting molecules. An evaluation of the process greenness was performed. Conclusion: The method is potentially universally applicable for green acetylation of hydrophilic biological molecules, potentially easily scalable for industrial applications, including pharmaceutical, cosmetic and food industry.

Full text of DOI:10.3762/bjoc.12.214

Tunable microwave-assisted method for the solvent-free and
catalyst-free peracetylation of natural products
Manuela Oliverio*1,2, Paola Costanzo1, Monica Nardi3, Carla Calandruccio1,
Raffaele Salerno2 and Antonio Procopio1,2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2016, 12, 2222–2233.
1Department of Health Science, University Magna Graecia of
Catanzaro, Viale Europa, Loc. Germaneto, 88100 Catanzaro, Italy,
2InterRegional Center for Food Safety and Health, University Magna
Graecia of Catanzaro, Viale Europa, Loc. Germaneto, 88100
Catanzaro, Italy and 3Department of Chemistry, Università della
Calabria, Cubo 12C, 87036-Arcavacata di Rende (CS), Italy
doi:10.3762/bjoc.12.214
Received: 08 July 2016
Accepted: 29 September 2016
Published: 20 October 2016
This article is part of the Thematic Series "Green chemistry".
Guest Editor: L. Vaccaro
Email:
Manuela Oliverio* - m.oliverio@unicz.it.
* Corresponding author
© 2016 Oliverio et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
catalyst-free; microwaves; peracetylation; polyhydroxylated
compounds; solvent-free
Abstract
Background: The peracetylation is a simple chemical modification that can be used to enhance the bioavailability of hydrophilic
products and to obtain safe and stable pro-drugs.
Results: A totally green, solvent-free and catalyst-free microwave (MW)-assisted method for peracetylation of natural products
such as oleuropein, alpha-hederin, quercetin and rutin is presented. By simply tuning the MW heating program, polyols with chemi-
cal diverse –OH groups or thermolabile functionalities can be peracetylated to improve the biological activity without degradation
of the natural starting molecules. An evaluation of the process greenness was performed.
Conclusion: The method is potentially universally applicable for green acetylation of hydrophilic biological molecules, potentially
easily scalable for industrial applications, including pharmaceutical, cosmetic and food industry.
Introduction
Peracetylation of alcohols, phenols and amino groups is a clas- Several in vitro and in vivo studies on peracetylated derivatives
sical protection method in multistep syntheses as well as a tran- of natural products demonstrated that peracetylation increases
sient chemical modification to improve the bioavailaibility and the cell intake, the intragastric absorbance and the oral bioavail-
bioactivity of hydrophilic drugs and natural polyols [1-9]. ability in respect to the unprotected natural compound [2,3,8,9].
2222

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
It has been hypothesized that peracetylated molecules can molecules or natural products. Between them a crucial report
exploit the same pathway than unprotected molecules to pass about the MW-assisted solvent-free and catalyst-free acety-
the cell membrane [5] and, once inside the cells, acetyl groups lation of anthranilic acid using acetic anhydride as acetylating
can be removed by intracellular esterases thus resulting in agent, kept our attention [26]. According to this report, few
an augmented dose of active principle [2,3]. Moreover, minutes at maximum MW power (1000 Watt), without any tem-
peracetylation affects the pharmacokinetics by prolonging the perature control, are needed to quantitative acetylate anthranilic
half-life of the unprotected molecules whose hydroxy groups acid. Obviously such uncontrolled conditions are not suitable
are unstable in neutral, slight alkaline or oxidative environ- for natural molecules, as they are often characterized by differ-
ments [4]. Furthermore, acetylation is a chemical modification ent moieties bonded each other by thermo or acid/base labile
well accepted in a biological environment, being the N-acety- ester bonds; nevertheless such report furnished us the proof of
lation, N,O-acyl transfer and the deacetylation some of the principle that the rapid rise of temperature due to MW can cata-
metabolic processes mediated by cytosolic and mitochondrial lyse acetylation using acetic anhydride. So, starting from this
acetyl-CoA dependent enzymes, naturally addressed to lower statement and trading on our experience in catalyst-free reac-
the adverse biological effects or to ameliorate the biological tions [27,28] and MW-assisted chemistry [29-35], we propose
response of several drugs [10]. Besides, well-known commer- here a universal MW-assisted method for peracetylation of
cial drugs, such as acetylsalicylic acid (Aspirin), are acetylated multifunctional compounds. The method is totally green and
molecules thus demonstrating that peracetylation has been ap- safe as it employs food grade acetic anhydride as acetylating
proved by the FDA (Food and Drug Administration). Even the agent, solvent-free and catalyst-free conditions, an easy work-
EFSA (European Food Safety Agency) accepted peracetylation up procedure affording the peracetylated molecules without any
as a method to improve the solubility of natural ingredients in chromatographic purification. The possibility to contemporary
fatty matrix (peracetylated starches are labeled as E1420 in the acetylate several chemically diverse –OH groups on thermola-
Union list of Food Additives) [11].
bile molecules simply tuning the heating program on the
MW-oven is discussed.
Classically peracetylation reactions have been performed by
treatment of alcohols and phenols with acid anhydrides or acid Results and Discussion
chlorides in the presence of bases [12]. Recently, the urgency to Our work started from the results reported in literature for the
find more environmental benign methods for standard transfor- MW-assisted acetylation of anthranilic acid. As the water
mations, led to the optimization of methods employing prefer- content can be a limiting factor for the acetylation equilibrium,
ably acetic anhydride in solvent free conditions, in presence of a pre-drying procedure is often required before the use of acetic
non-toxic homogeneous catalysts such as environmental safe anhydride [26]. In order to optimize a cheap, safe, green and
Lewis acids [13,14]. Moreover, the need to easily recover and easily scalable method for industrial application we decided to
reuse the catalyst, thus reducing the work-up procedure to a use food grade acetic anhydride (Eastman) as acetylating agent,
simple filtration, resulted in the growing use of heterogeneous after its anhydrification by simple passing it through a bed of
or supported catalysts [15-17], solid nanopowders or nanoparti- activated molecular sieves under nitrogen steam. Such anhydri-
cles [18,19], non-metal-based heterogeneous acetylation cata- fication technique was already proposed for several organic sol-
lysts [20-22], as well as natural marine clays instead of homo- vents as safer alternative to classical methods using reactive
geneous catalysts as reaction activators [23]. Even if these metals, metal hydrides or solvent distillation [36].
methods allow a complete peracetylation of several functionali-
ties at room temperature in good to excellent yields, it is worth Moreover, in order to explore the versatility of the methodolo-
noting that some of them use metal-based catalysts needing gy we selected a set of representative molecules of different
long preparation procedures, or in the case of non-metal-based categories (Figure 1) such as pharmaceuticals (salicylic acid (2),
catalysts, inorganic acids are employed to activate acylation. On paracetamol (7) and salbutamol (9)), cosmetic ingredients
the other hand, the increasing attention to the final product (cytronellol (6) and myrtenol (10)), biomolecules (cholesterol
safety, strictly connected to the consumers safety and health, (3), N-Boc- tyrosine methyl ester (8), uridine (12) and methyl-
push the pharmaceutical and food companies to prefer methods α-D-glucopyranoside (11)) and natural antioxidant compounds
that allows to minimize the opportunity of the final product to in their simple (hydroxytyrosol (4), homovanillic alcohol (5),
get in touch with chemical additives. At the best of our know- quercetin (13)) or glycosylated forms (oleuropein (14), rutin
ledge, only few reports exist dealing with the acetylation of (17), alpha-hederin (16)). Because of their heterogeneity in
hydroxy groups under catalyst-free conditions. Most of them terms of thermostability, number and reactivity of –OH groups,
use alternative acetylating agents [24] or alternative energy we decided to split the complete set in four subsets: molecules
sources [25], but none of them has been applied to complex characterized by a good thermostability with up to three –OH
2223

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
Figure 1: Chemical structures of bioactive substrates and their partition in subsets.
groups (non thermolabile compounds, NTC), molecules charac- lecular sieves to preserve dryness. Moreover, it has been re-
terized by a strong thermolability (thermolabile compounds, ported that molecular sieves can have a role in acetylation reac-
TC), complex molecules characterized by at least two different tion, both under classical or alternative heating mode, thanks to
chemical moieties and/or more than 3 –OH groups, (complex their soft base character and MW absorbing power, respective-
polyols, CP) and complex molecules with a disaccharide ly [37-40]. The reaction performed without molecular sieves
moiety, namely carrying a huge number of chemically different gave rise to worse results (data not shown), even if a catalytic
–OH groups (di-glycosylated complex polyols, DGCP). To set role could not be proved in our case, because the reactions were
the reaction conditions we used the compounds belonging to the activated and gave rise to moderate yields as in a typical equi-
NTC group (2–9, Figure 1) comparing the obtained results to librium system.
the literature reported for the anthranilic acid (1).
The reactions were monitored by TLC or GC–MS until the
All the molecules were reacted in a Synthos 3000 (Anton-Paar) reagent disappeared and the work-up procedure was optimized
microwave oven equipped with an external IR sensor for the in order to minimize the wastes of the process. Namely the reac-
temperature control; they were solubilized in dry acetic an- tion mixture was reacted with ethanol in order to eliminate the
hydride in a concentration of 0.1 mmol/mL without any other excess of acetic anhydride thus producing acetic acid and
solvent or catalyst, in presence of the 10% w/w of activated mo- AcOEt, a common organic solvent with acceptable safety and
2224

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
environmental characteristics [41], recoverable by simple evap- The internal temperature profiles corresponding to each
oration under reduced pressure. After evaporation, the acetic P-program are depicted in Figure 2.
acid was neutralized by adding a saturated solution of NaHCO3
and the acetylated products were recovered by decantation with- The yields of the obtained peracetylated products (Table 2) are
out any other purification. The water solution of NaOAc ob- referred to isolated compounds, that have been fully character-
tained as byproduct can be reused as component for buffer solu- ized by HRMS, 1H and 13C NMR when unknown. The sub-
tions or as pickling agent for foods [11]. A complete scheme of strates giving rise to a mixture of inseparable acetylated deriva-
the reaction protocol is depicted in Scheme 1.
tives were identified by LC/HRMS. In particular, UHPLC
combined with an Orbitrap mass spectrometer at high resolving
power, enabled the detection and the accurate mass measure-
ment (<5 ppm error) of all the acetylated analytes in the mix-
ture. The yields have been calculated on the peak intensities
selecting the analytes having an ion current intensity value
10 fold lower than the main product. A little portion of the mix-
ture was purified by flash chromatography for the structural
characterization of the major product.
As it is reported in Table 2 we obtained good to excellent yields
of acetylated products for all the substrates belonging to NTC
group. More than one reaction cycle was needed when the reac-
tant had a low solubility in acetic anhydride as in the case of
Scheme 1: Solvent-free and catalyst-free MW-assisted acetylation
protocol.
Concerning the microwave settings we decided to extend the cholesterol, N-Boc-tyrosine methyl ester and salbutamol
reaction time in respect to the reported acetylation of anthranilic (entries 3, 8 and 9, Table 2). Comparing to data reported in the
acid [26] and to carefully monitor the microwave power, thus literature [42,43], the modest yields of peracetylated product
realizing a simple P-controlled program, corresponding to an obtained in case of cholesterol 3 and salbutamol 9 were
internal temperature program, to softly reach the maximum balanced by the absence of catalyst and by the reaction speed
power. An adjustment of the NCT P-program settings was per- due to microwaves. The applied P-program was compatible
formed for the other subsets, characterized by more instable or with the N-Boc protecting group already present on the tyrosine
complex molecules, as it is described in Table 1.
methyl ester 8. Concerning salbutamol (9) the reported yield
Table 1: P-controlled MW programs for peracetylation of compounds listed in Figure 1 (Synthos 3000, equipped with 64-MG5 rotor).
Entry
1
Method
NTC
Time (min)
Power (W)
Tinternal (°C)a
TIR (°C)
0 → 5
5 → 17
17 → 20
0 → 300
300
0
25 → 100
100
100 → 25
85
2
3
4
TC
CP
0 → 2
2 → 7
7 → 12
12 → 22
22 → 25
0 → 130
130
130 → 300
300
0 → 60
60
60 → 100
100
50
50
85
85
85
300 → 0
100 → 25
0 → 5
5 → 10
10 → 12
12 → 62
62 → 65
0 → 300
300
300 → 400
400
0 → 100
100
100 → 120
120
85
85
105
105
105
0
120 → 25
DGCP
0 → 5
5 → 10
0 → 300
300
25 → 100
100
85
85
10 → 15
15 → 45
45 → 50
50 → 90
90 → 93
300 → 400
400
400 → 500
500
100 → 120
120
120 → 145
145
105
105
120
120
120
500 → 0
145 → 25
a Internal reaction temperature, related to IR limit temperature by the following equation: Tinternal = 1.214 × TIR. Maximum internal temperature for
each category was established between many, by controlling the cleanness of the reaction profile.
2225

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
Figure 2: MW-assisted acetylation T-program for different subset of substrates.
was referred to the peracetylated product 9a even if a quantita- the first acetylation run, surprisingly gave a complex mixture of
tive conversion was registered and the obtained mixture of dif- differently acetylated forms (Figure 3), among them the di-O-
ferent acetylated derivatives was fully identified by GC–MS acetylated quercetin 13a was the major product (60% of the
(see Supporting Information File 1). In this last case the change total reaction products, entry 13, Table 2).
of the P-program was ineffective in increasing the yield of 9a in
respect to the other acetylated forms (data not shown).
As the permeability and/or bioavailability of polyols is in-
creased, no matter if the molecules are fully or partially acety-
As it can be argued by Figure 2 and Table 1, that the TC lated, we decided to identify the full mixture by LC–MS analy-
program (entry 2, Table 1) characterized by an intermediate step sis. We also provided a purification of the major product in
at lower temperature was necessary to avoid the degradation of order to carry out a structural characterization and to determine
TCs when exposed to the NTC program. In our case only a sub- the yield of isolated product. Figure 3 shows the LC–HRMS of
strate, namely myrtenol (10), characterized by an allyl alcohol O-acetylated quercetin reaction mixture (for 1H and 13C NMR
moiety, needed this softer program to be acetylated without spectra of the mixture see Supporting Information File 1).
degradation and/or polymerization (entry 10, Table 2).
Chemical structures of non-fully acetylated forms, i.e., tetra-O-
acetylated-quercetin (8% of the mixture, entry B, Figure 3),
Molecules bearing more than three –OH groups (CPs), besides di-O-acetylated quercetin (60% of the mixture, entry C,
N- or O- glycosidic bonds, needed a program composed of two Figure 3), tri-O-acetylated quercetin (7% of the mixture, entry
steps with increasing temperature and power to complete (entry D, Figure 3), mono-O-acetylated-quercetin (25% of the mixture,
3, Table 1). During the first step, where the MW conditions are entry E, Figure 3), could not be univocally assigned, except for
very similar to NTC program, the more reactive –OH groups, the major product, characterized by 1H NMR. The mixture of
such as primary or non-hindered phenolic groups, were acety- the acetylated forms can in principle work as bioactive compo-
lated, while a second step at higher power and temperature nent when used as crude reaction miture without purification.
(Figure 2) was needed to realize the acetylation of all the –OH
functionalities. The two-step temperature increase allowed to Comparable results in terms of conversion to those collected for
activate the reaction, limiting the exposure time of such com- the CP group were obtained with the last group of molecules
pounds to the program higher temperature, thus preserving (DGCPs, entries 15–17, Table 2). Nevertheless, DGCP needed a
sensitive bonds.
MW three steps program, reaching the maximum power of
500 W (entry 4, Table 1), due to the increased number of chem-
All the polyols were peracetylated in good yields (entries ical diverse –OH groups. In all cases a mixture of different acet-
11–14, Table 2), even if in some cases more than one reaction ylated forms were obtained and the prevalence of the peracety-
cycle was necessary for complete conversion (entries 11, 12, 15, lated product was inversely proportional to the number of –OH
16 and 17, Table 2). The only exception was the natural prod- groups within the molecule. So, good yields of peracetylated
uct quercetin (13) that, despite a quantitative conversion after product 16a were obtained from α-hederin (entry 16, Table 2),
2226

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
Table 2: Solvent free and catalyst free peracetylation MW assisted of alcohols and polyols.
Entry
Path
Product
Conv.
(%)a
Yield
(%)b
N° Run
1
NTC
100
100
100
100
1
1a
2a
2
3
NTC
NTC
1
3
70
62
3a
4a
5a
4
5
NTC
NTC
100
100
100
100
1
1
6
NTC
100
100c
1
6a
7a
7
8
NTC
NTC
95
93
95
1
2
100
8a
9a
9
NTC
100
30d
3
2227

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
Table 2: Solvent free and catalyst free peracetylation MW assisted of alcohols and polyols. (continued)
10
11
TC
CP
100
100
100
1
2
10a
11a
70d,e
12
CP
100
92d,e
2
12a
13
14
CP
CP
94
60d
100
1
1
13af
100
14a
15
DGCP
100
50d,e
2
15a
16
DGCP
100
85d,e
2
16a
2228

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
Table 2: Solvent free and catalyst free peracetylation MW assisted of alcohols and polyols. (continued)
17
DGCP
100
45e
2
17a
aConversion determined by GC–MS or LC–MS and calculated as (100 − % area under the reagent peak). bIsolated products. cVolatile product. dA mix
of acetylated forms has been obtained. The yield was determined on the major product after purification eFresh Ac2O added before each cycle. fMajor
isobar form from LC–MS. No attribution about the position of acetyl groups was made.
Figure 3: LCHRMS (m/z, [M + Na]+ and [M − H]− only for entry F) spectrum of O-acetylated quercetin (reaction mix) in total ion current (TIC, entry A)
and extract ion Current (XIC, entries B–F) relative to main acetylated-forms: tetra-O-acetylated quercetin (8% of the mixture, entry B), di-O-acetylated
quercetin (60% of the mixture, entry C), tri-O-acetylated quercetin (7% of the mixture, entry D), mono-O-acetylated-quercetin (25% of the mixture,
entry E). The conversion was estimated around 96%, because of the presence of 6% of unreacted quercetin (entry F).
while medium yields were obtained for peracetylated-β-D- An evaluation of the greenness of the process was performed by
lactose 15a (entry 15, Table 2) and peracetylated rutin 17a calculation of atom economy (AE), reaction mass efficiency
(entry 17, Table 2) where the remaining 50% of product was (RME), mass intensity (MI) and mass productivity (MP), ac-
constituted by a mixture of different non-fully acetylated forms, cording to the definition summarized by Constable et al. [44]
even after more than one acetylation run. Moreover, peracetyla- (see Supporting Information File 1). The values for all the
tion of rutin (17), which is the di-glycosylated derivative of previous parameters, calculated for the 17 performed reactions,
quercetin (13), demonstrated that an additional acetylation run are reported in Table 3. AE was referred to the peracetylated
could give rise also to a quercetin peracetylation.
compound, as it was the reaction desired product.
2229

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
Conclusion
Table 3: Process green chemistry metrics.
In conclusion, a solvent-free and catalyst-free MW-assisted
method of peracetylation of natural polyols has been proposed.
The method is high versatile such it can be applied to alcohols,
phenols and polyols characterized by a huge chemical diversity
and thermostability, simply tuning the MW settings. Such
method is potentially universally applicable for green acety-
lation of hydrophilic biological molecules, thus improving their
bioavailability and biological activity, no matter if they are
simple polyphenols or glycosilated molecules. Thanks to the
absolute absence of toxic reactants and byproducts the method
is potentially easily scalable for industrial applications, includ-
ing pharmaceutical, cosmetic and food industry, where the eco-
compatibility of the reaction conditions, the easy waste manage-
ment and the product safety are pivotal conditions for market.
Entry Yield (%) AE (%) RME (%)
MI
MP (%)
1
2
100
100
62
75
75
88
61
68
77
76
85
67
76
51
67
76
75
58
70
63
75
75
54
61
68
42
71
76
20
76
36
62
46
75
29
59
28
2
2
3
2
2
3
2
2
7
2
3
2
3
2
5
3
6
50
50
33
50
50
33
50
50
14
50
33
50
33
50
20
33
16
3
4
100
100
55
5
6
7
93
8
90
9
30
10
11
12
13
14
15
16
17
100
70
92
60
100
50
Experimental
Materials and methods
MW-assisted reactions were performed in Synthos 3000 instru-
ment from Anton Paar, equipped with a 64MG5 rotor and an IR
probe as external control of the temperature. Using a tempera-
ture-controlled program the instrument is able to tune the power
85
45
As expected, RME is a more realistic parameter than AE due to magnetron in order to reach and to maintain the fixed tempera-
the influence of the reaction yield. Because MI and MP ture throughout the experiment. For each run 16 positions of the
consider all the masses implied in the process and take into rotor was occupied by 0.3–3 mL glass vials sealed with a dedi-
account yield, solvents and reaction auxiliaries, they are more cated PEEK screw-cup together with a reliable PTFE seal.
useful parameters to evaluate the sustainability of the process Reactions were monitored by TLC using silica plates 60-F264
from an industrial point of view [44]. For the calculation of MI on alumina, commercially available from Merk. GC–MS spec-
and MP the reaction work-up was included as a reaction step tra were recorded on a GC–MS Thermo Scientific workstation,
(see Supporting Information File 1) because the products ob- formed by a Focus GC (30-m VARIAN-VF-5ms, 0.25 mm di-
tained by the hydrolysis of the excess of Ac2O used, both as ameter capillary column, working on spitless mode, 1.2 mL/min
reaction reagent and solvent, are useful chemicals. The calcu- He as carrier gas) and by an DSQ II mass detector. Chromatog-
lated values were good, thus demonstrating the versatility and raphy was performed using a Thermo Scientific Dionex Ulti-
sustainability of the process. Our prevision shows how the mate 3000 RS, injecting directly onto a Thermo Scientific
process remains reasonable in terms of mass productivity, Hypersil Gold C18 column (50 × 2.1 mm, 1.9 µm particle size),
ranging from 16% to 50%.
equilibrated in 95% solvent A (0.1% aqueous solution of formic
acid), 5% solvent B (methanol). The column and auto-sampler
Finally a scaled protocol extended to the maximum oven temperatures were maintained at 24 °C and 20 °C, respectively.
capacity was tested using oleuropein (14) as test compound. The elution flow rate was 600 µL/min by linearly increasing the
30 mL vials were reacted in the Synthos 3000 XF-100 rotor, concentration of solvent B from 5 to 55% in 4 min, from 55% to
after filling each vial with a ten-fold quantity of reactants, 95% in 2 min and remaining for other 2 minutes in isocratic
reaching a total processed oleuropein of 8 g/reaction cycle. flow, then returning to 5% in 1 minute. At the end it was
Table S2 in Supporting Information File 1 shows the power- re-equilibrated for 3 minutes. The total run time, including
controlled MW protocol, adjusted in respect to the small-scale column wash and equilibration was 15 min. A Thermo Scien-
procedure. Figure S3 reports a comparison between the temper- tific Q-ExactiveTM mass spectrometer was used for HRMS
ature profiles of the small and large scale peracetylations: the measurements using electrospray as ionization source with both
two curves are comparable, even if a better stability is regis- negative and positive polarities, at a resolving power of 35.000
tered for the experiment performed in small scale. Nevertheless, (defined as FWHM at m/z 200), IT = 100 ms, and ACG
the large-scale process successfully produced 10 g of peracety- target = 500.000, by full scan analysis (mass range
lated oleuropein in 65 minutes (see Supporting Information 140–900 amu for 2 samples and 200–1500 amu for other 2 sam-
File 1).
ples). Source conditions were: spray voltage 2.9 kV, sheath gas:
2230

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
30, arbitrary units, Auxiliary gas: 10, probe heater temperature: CH2=CH=O] (10), 192+ [M − CH3CO2H] (1), 150 [C11H12O3+
280 °C; capillary temperature: 320 °C; S-Lens RF Level: 50. − CH2=CH=O] (100), 135 [C9H9O+ − CH3] (20); 1H NMR
The instrument was calibrated by Thermo calibration solutions (300 MHz, CDCl3, 25 °C, TMS) δ 6.97 (d, JG-H = 8 Hz, 1H,
prior to the beginning the analysis. 1H and 13C spectra were re- HH), 6.81 (s, 1H, HF), 6.80–6.78 (d, J = 8 Hz, 1H, HG),
corded on a Bruker WM 300 instrument on samples dissolved 4.31–4.25 (t, JD-E = 7 Hz, 1H, HD), 3.82 (s, 3H, HB), 2.95–2.89
in CDCl3. Chemical shifts are given in parts per million (ppm) (t, JD-E = 7 Hz, 1H, HE), 2.30 (s, 3H, HA), 2.03 (s, 3H, HC);
from tetramethylsilane as the internal standard (0.0 ppm). Cou- 13C NMR (75 MHz, CDCl3, 25 °C, TMS) δ 171.3, 169.4,
pling constants (J) are given in Hertz. All new compounds were 151.3, 138.7, 137.0 123.0, 121.3, 113.4, 65.0 56.2, 35.3, 21.3,
characterized by HRMS, 1H NMR and 13C NMR, while known 21.0.
compounds were analysed by comparison with the data coming
from literature [14,45-47]. All chemicals were used as commer- Acetyl salbutamol (9a): Yellow oil; inseparable mixture;
cially available.
pracetylated salbutamol (major product): Yield 30%; MS
(70 eV, IE) m/z (%): 365 [M+] (0.5), 249 [M+ − CH3COOCH3-
A request for an Italian Patent concerning the present protocol CH2=C=O] (10), 188 [M+ − 3 × CH3COO] (10), 146
was submitted by the authors of this article (request number [C13H17NO+ − t-Bu] (20), 86 [CH2=NHt-Bu+] (100); 1H NMR
n° 102016000052914, registration date 23/05/2016).
(300 MHz, CDCl3, 25 °C, TMS) δ 7.39 (d, JG-I = 2 Hz, 1H,
HG), 7.33–7.30 (dd, JG-I = 2 Hz, JH-I = 8.3 Hz, 1H, HI),
7.16–7.09 (d, JH-I = 8.3 Hz, 1H, HI), 5.96–5.88 (dd, JF-E = 3.4
General procedure for Ac2O purification
The acetic anhydride (food grade, Eastman) was dried prior to Hz, JF-E’ = 10 Hz, 1H, HF), 3.84–3.72 (dd, JE-E’ = 16.3 Hz,
use through the following procedure: a glass column under N2 JF-E’ = 10 Hz, 1H, HE’), 3.59–3.49 (dd, JE-E’ = 16.3 JF-E = 3.4
was filled with 4 Å molecular sieves pre-activated at 350 °C Hz, 1H, HE), 2.34 (s, 3H, HB), 2.23 (br s, 1H, NH), 2.11 (s, 3H,
overnight. The acetic anhydride was passed through the sieves HC), 2.08 (s, 3H, HA), 1.49 (s, 9H, HD); 13C NMR (75 MHz,
3 times and collected in a flask under N2. The collected an- CDCl3, 25 °C, TMS) δ 171.4, 170.9, 170.1, 169.5, 149.6, 136.3,
hydride was gently stirred over 20% w/w of activated molecu- 129.2, 129.1, 128.7, 127.8, 123.7, 61.5, 57.8, 51.2, 29.5, 25.8,
lar sieves for 48 hours, before the use.
21.4, 21.2.
Optimized MW-assisted peracetylation
Acetylated Quercetin (13a): Yellow powder; inseparable mix-
The substrate belonging to one of the subset reported in Table 1 ture; di-O-acetylated quercetin (major product): Yield 60%;
(NTC, TC, CP, DGNP) (0.1 mmol) was left to react under MW HRMS: [M + Na+] m/z: 451.0635 (theoretical [M + Na+] m/z:
heating (Synthos 3000, Anton Paar) with dry acetic anhydride 451.0636); 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ 2.336
(1 mL, 10 mmol) in a 3 mL vial (Rotor 64MG5 ), equipped with (s, 3H, Ac), 2.3381 (s, 3H, Ac), 2.3432 (s, 3H, Ac), 2.3483 (s,
a magnetic stirrer in the presence of molecular sieves 3H, Ac), 6.86 (d, Jmeta= 2.19 Hz, 1H, HE), 7.34 (d, Jmeta= 2.19
(10 % w/w). The microwave, equipped with IR sensor for Hz, 1H, HA), 7.37, (d, Jortho= 8.6 Hz, 1H, HD), 7.64 (d, Jmeta=
external temperature control (IR limit calculated as follows: 2.19 Hz, 1H, HB), 7.74 (dd,, Jortho= 8.6Hz, Jmeta= 2.19 Hz, 1H,
Tinternal = 1.214 × TIR), has been set with the power programs HC); 13C NMR (75 MHz, CDCl3, 25 °C, TMS) δ 20.9, 21.0,
provided for its subset as described in Table 1. At the end of the 21.4, 21.5, 109.3, 114.2, 124.2, 124.3, 126.8, 128.14, 131.2,
reaction, the mixture was filtered, diluted with ethanol (2 mL) 142.6, 144.7, 150.8, 154.6, 157.2, 168.1, 168.2, 170.4.
and left under vigorous stirring for 30 minutes at 50 °C. The
mixture was then evaporated under reduced pressure and a Peracetylated α-hederine (16a) yellow oil: Yield 85%; HRMS:
small amount of a saturated solution of sodium bicarbonate [M + Na+] m/z: 1025.5045 (theoretical [M + Na+] m/z:
(3.8 mL, 10 mmol NaHCO3) was added. After the evolution of 1025.5080); 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ 0.73
CO2, the precipitation of the peracetylated product was ob- (s, 3H, HA), 0.79 (s, 3H, HB), 0.90 (s, 3H, HH), 0.92 (s, 3H,
served. The products were separated by simple decantation. For HL), 0.95 (s, 3H, HQ), 1.10 (s, 6H, HG,J’), 1.23 (d, JO-N = 6.6
compounds which do not precipitate upon addition of NaHCO3, Hz, 2H, HO), 1.29–1.90 (m, 20H, HC,D,E,F,I,J,P,S,V,K,R), 2.01 (s,
an extraction with AcOEt was needed. The organic phase, after 3H, Ac), 2.03 (s, 3H, Ac), 2.06 (s, 3H, Ac), 2.10 (s, 3H, Ac),
drying with Na2SO4, filtration and evaporation, gave the reac- 2.11 (s, 3H, Ac), 2.14 (s, 3H, Ac), 2.82 (m, 1H, HU), 3.85–3.98
tion crude.
(m, 2H, HK, HE’), 4.07–4.17 (m, 4H, 1HE’, HB’,F’,L’), 4.43 (d,
JN-O = 6.6 Hz, 2H, HN), 4.95–5.07 (m, 4H, HC’,D’,G’,J’),
5.22–5.30 (m, 3H, HA’,T,I’); 13C NMR (75 MHz, CDCl3, 25 °C,
Characterization of selected compounds
Peracetylated homovanillic alcohol (5a): Yellow oil; Yield TMS) δ 182.8, 170.4, 170.3, 170.1, 170.0, 169.6, 143.6, 122.4,
100%; MS (70 eV, IE) m/z (%): 252 [M+] (1), 210 [M+ − 103.5, 98.2, 81.9, 71.0, 69.5, 68.6, 67.8, 67.1, 62.6, 47.8, 46.4,
2231

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
4. Lam, W. H.; Kazi, A.; Kuhn, D. J.; Chow, L. M. C.; Chan, A. S. C.;
Doub, Q. P.; Chana, T. H. Bioorg. Med. Chem. 2004, 12, 5587–5593.
doi:10.1016/j.bmc.2004.08.002
45.8, 41.9, 41.5, 41.0, 39.2, 38.3, 36.5, 33.7, 33.0, 32.4, 30.6,
27.5, 25.7, 25.4, 23.5, 23.4, 22.8, 20.9, 20.6, 17.9, 17.3, 16.9,
15.8, 12.6.
5. Colin, D.; Lancon, A.; Delmas, D.; Lizard, G.; Abrossinow, J.; Kahn, E.;
Jannin, B.; Latruffe, N. Biochimie 2008, 90, 1674–1684.
doi:10.1016/j.biochi.2008.06.006
Peracetylated rutine (17a): Brown powder: Yield 45%; HRMS:
[M + Na+] m/z: 1053.2470 (theoretical [M + Na+] m/z:
1053.2482); 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ 1.05
(d, JL’K’ = 6.25 Hz, 3H, HL’), 1.58 (s, 3H, Ac), 1.94 (s, 3H,
Ac), 1.95 (s, 3H, Ac), 2.02 (s, 3H, Ac), 2.08 (s, 3H, Ac), 2.14
(s, 3H, Ac), 2.29 (s, 3H, PhOAc), 2.34 (s, 3H, PhOAc), 2.35 (s,
6. Higgs, G. A.; Salmon, J. A.; Henderson, B.; Vane, J. R.
Proc. Natl. Acad. Sci. U. S. A. 1987, 84, 1417–1420.
doi:10.1073/pnas.84.5.1417
7. Bulotta, S.; Corradino, R.; Celano, M.; Maiuolo, J.; D’Agostino, M.;
Oliverio, M.; Procopio, A.; Filetti, S.; Russo, D. J. Mol. Endocrinol.
2013, 51, 181–189. doi:10.1530/JME-12-0241
3H, PhOAc), 2.44 (s, 3H, PhOAc), 3.56–3.67 (m, 1H, HE’), 8. Bulotta, S.; Corradino, R.; Celano, M.; D’Agostino, M.; Maiuolo, J.;
Oliverio, M.; Procopio, A.; Iannone, M.; Rotiroti, D.; Russo, D.
3.50–3.54 (m, 2H, HF’’,J’), 4.91–4.97 (m, 2H, HI’,D’), 5.05–5.09
Food Chem. 2011, 127, 1609–1614.
(m, 2H, HB’,H’), 5.14–5.20 (m, 1H, HC’), 5.26 (d, JF’F’’ = 9.32
doi:10.1016/j.foodchem.2011.02.025
Hz, 1H, HF’), 5.42, (d, JG’H’ = 7.67 Hz, 1H, HG’), 5.41 (d, JA’B’
9. Lepore, S. M.; Morittu, V. M.; Celano, M.; Trimboli, F.; Oliverio, M.;
= 7.7 Hz, 1H, HA’), 6.84 (d, Jmeta = 2.19 Hz, 1H, HE), 7.31 (d,
Procopio, A.; Di Loreto, C.; Damante, G.; Britti, D.; Bulotta, S.;
Jmeta = 2.19 Hz, 1H, HA), 7.35, (d, Jortho = 8.6 Hz, 1H, HD),
7.90 (d, Jmeta= 2.19 Hz, 1H, HB), 7.95 (dd, Jortho = 8.6 Hz, Jmeta
= 2.19 Hz, 1H, HC); 13C NMR (75 MHz, CDCl3, 25 °C, TMS)
δ 14.38, 17,52, 21.02 (×4), 21.42, 21.50, 23.33, 24.11, 29.27,
30.05, 30.72, 39.09, 66.68, 67.30, 68.51, 69.35, 69.72, 69.85,
71.24, 71.74, 72.90, 98.09, 99.94, 109.37, 113.77, 115.42,
Russo, D. Int. J. Endocrinol. 2015, No. 431453.
doi:10.1155/2015/431453
10.King, C. M.; Glowinski, I. B. Environ. Health Perspect. 1983, 49, 43–50.
doi:10.1289/ehp.834943
11.Annex III to Regulation (EC) No 1333/2008: Union list of food additives
approved for use in food additives, food enzymes, food flavourings and
nutrients.
123.80, 125.03, 127.57, 128.93, 137.28, 142.12, 144.44, 150.53, 12.Horton, D. In Organic Synthesis Collective Volume 5;
Baumgarten, H. E., Ed.; John Wiley & Sons: NewYork, 1973; 1ff.
154.30, 155.00, 156.96, 168.07, 168.21, 168.39, 169.59, 169.93,
13.Dalpozzo, R.; De Nino, A.; Maiuolo, L.; Oliverio, M.; Procopio, A.;
170.07, 170.23, 170.41.
Russo, B.; Tocci, A. Aust. J. Chem. 2007, 60, 75–79.
doi:10.1071/CH06346
14.Procopio, A.; Alcaro, S.; Nardi, M.; Oliverio, M.; Ortuso, F.;
Supporting Information
Sacchetta, P.; Pieragostino, D.; Sindona, G. J. Agric. Food Chem.
2009, 57, 11161–11167. doi:10.1021/jf9033305
Supporting Information File 1
15.Satam, J. R.; Jayaram, R. V. Catal. Commun. 2008, 9, 2365–2370.
Scaled oleuropein peracetylation procedure, GC–MS,
doi:10.1016/j.catcom.2008.05.033
LC–HRMS, 1H and 13C NMR spectra of new compounds,
16.Rajabi, F. Tetrahedron Lett. 2009, 50, 395–397.
as well as calculation for green chemistry metrics.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-12-214-S1.pdf]
doi:10.1016/j.tetlet.2008.11.024
17.Zareyee, D.; Ghadikolaee, A. R.; Khalilzadeh, M. A. Can. J. Chem.
2012, 90, 464–468. doi:10.1139/v2012-018
18.Farhadi, S.; Zaidi, M. J. Mol. Catal. A: Chem. 2009, 299, 18–25.
doi:10.1016/j.molcata.2008.10.013
19.Farhadi, S.; Panahandehjoo, S. Appl. Catal., A 2010, 382, 293–302.
doi:10.1016/j.apcata.2010.05.005
Acknowledgements
This work was supported by the grant POR Calabria FSE 2007/
2013, Asse IV "Capitale Umano", Obiettivo Operativo M.2.,
Piano d'azione 2011-2013- Department 11 "Cultura-Istruzione-
Università-Ricerca-Innovazione Tecnologica-AltaFormazione"
of Regione Calabria.
20.Niknam, K.; Saberi, D. Tetrahedron Lett. 2009, 50, 5210–5214.
doi:10.1016/j.tetlet.2009.06.140
21.Shimizu, K.-i.; Higuchi, T.; Takasugi, E.; Hatamachi, T.; Kodama, T.;
Satsuma, A. J. Mol. Catal. A: Chem. 2008, 284, 89–96.
doi:10.1016/j.molcata.2008.01.013
22.Das, B.; Thirupathi, P. J. Mol. Catal. A: Chem. 2007, 269, 12–16.
doi:10.1016/j.molcata.2006.12.029
References
23.Sreedhar, B.; Arundhathi, R.; Amarnath Reddy, M.; Parthasarathy, G.
Appl. Clay Sci. 2009, 43, 425–434. doi:10.1016/j.clay.2008.10.001
24.Pelagalli, R.; Chiarotto, I.; Ferocia, M.; Vecchio, S. Green Chem. 2012,
14, 2251–2255. doi:10.1039/c2gc35485c
1. Green, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis,
3rd ed.; Wiley: NewYork, 1999; pp. 150ff.
2. Lambert, J. D.; Sang, S.; Hong, J.; Kwon, S.-J.; Lee, M.-J.; Ho, C.-T.;
Yang, C. S. Drug Metab. Dispos. 2006, 34, 2111–2116.
doi:10.1124/dmd.106.011460
25.Wang, X.-J.; Yang, Q.; Liu, F.; You, Q.-D. Synth. Commun. 2008, 38,
1028–1035. doi:10.1080/00397910701860372
3. Lee, S.-C.; Chan, W.-K.; Lee, T.-W.; Lam, W.-H.; Wang, X.;
Chan, T.-H.; Wong, Y.-C. Nutr. Cancer 2008, 60, 483–491.
doi:10.1080/01635580801947674
26.Wilhite, D. M.; Baldwin, B. W. J. Chem. Educ. 2002, 79, 1344.
doi:10.1021/ed079p1344
27.Cravotto, G.; Procopio, A.; Oliverio, M.; Orio, L.; Carnaroglio, D.
Green Chem. 2011, 13, 2806–2809. doi:10.1039/c1gc15756f
2232

Beilstein J. Org. Chem. 2016, 12, 2222–2233.
28.Oliverio, M.; Costanzo, P.; Paonessa, R.; Nardi, M.; Procopio, A.
RSC Adv. 2013, 3, 2548–2552. doi:10.1039/c2ra23067d
29.Procopio, A.; Gaspari, M.; Nardi, M.; Oliverio, M.; Tagarelli, A.;
Sindona, G. Tetrahedron Lett. 2007, 48, 8623–8627.
doi:10.1016/j.tetlet.2007.10.038
License and Terms
This is an Open Access article under the terms of the
Creative Commons Attribution License
30.Procopio, A.; De Luca, G.; Nardi, M.; Oliverio, M.; Paonessa, R.
Green Chem. 2009, 11, 770–773. doi:10.1039/b820417a
31.Procopio, A.; De Nino, A.; Nardi, M.; Oliverio, M.; Paonessa, R.;
Pasceri, R. Synlett 2010, 12, 1849–1853. doi:10.1055/s-0030-1258126
32.Oliverio, M.; Procopio, A.; Glasnov, T. N.; Goessler, W.; Kappe, C. O.
Aust. J. Chem. 2011, 64, 1522–1529. doi:10.1071/CH11125
33.Procopio, A.; Costanzo, P.; Curini, M.; Nardi, M.; Oliverio, M.;
Sindona, G. ACS Sustainable Chem. Eng. 2013, 1, 541–544.
doi:10.1021/sc4000219
(http://creativecommons.org/licenses/by/4.0), which
permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
(http://www.beilstein-journals.org/bjoc)
34.Oliverio, M.; Nardi, M.; Costanzo, P.; Cariati, L.; Cravotto, G.;
Giofrè, S. V.; Procopio, A. Molecules 2014, 19, 5599–5610.
doi:10.3390/molecules19055599
The definitive version of this article is the electronic one
which can be found at:
35.Oliverio, M.; Nardi, M.; Cariati, L.; Vitale, E.; Bonacci, S.; Procopio, A.
ACS Sustainable Chem. Eng. 2016, 4, 661–665.
doi:10.3762/bjoc.12.214
doi:10.1021/acssuschemeng.5b01201
36.Williams, D. B. G.; Lawton, M. J. Org. Chem. 2010, 75, 8351–8354.
doi:10.1021/jo101589h
37.Adinolfi, M.; Barone, G.; Iadonisi, A.; Schiattarella, M. Tetrahedron Lett.
2003, 44, 4661–4663. doi:10.1016/S0040-4039(03)01072-4
38.Sá, M. M.; Meier, L. Synlett 2006, 20, 3474–3478.
doi:10.1055/s-2006-958430
39.Cai, L.; Rufty, C.; Liquois, M. Asian J. Chem. 2014, 26, 4367–4369.
doi:10.14233/ajchem.2014.16573
40.Cardozo, H. M.; Ribeiro, T. F.; Sá, M. M.; Sebrão, D.;
Nascimento, M. G.; Silveira, G. P. J. Braz. Chem. Soc. 2015, 26,
755–764. doi:10.5935/0103-5053.20150037
41.Henderson, R. K.; Jiménez-González, C.; Constable, D. J. C.;
Alston, S. R.; Inglis, G. G. A.; Fisher, G.; Sherwood, J.; Binksa, S. P.;
Curzons, A. D. Green Chem. 2011, 13, 854–862.
doi:10.1039/c0gc00918k
42.Dalpozzo, R.; De Nino, A.; Maiuolo, L.; Procopio, A.; Nardi, M.;
Bartoli, G.; Romeo, R. Tetrahedron Lett. 2003, 44, 5621–5624.
doi:10.1016/S0040-4039(03)01358-3
43.Fenjan, A.-A. M.; Dhahir, S. A.; Al-Sahib, S. A.; Thanoon, S.
J. Al Nahrain University - Science 2011, 14, 50–57.
44.Constable, D. J. C.; Curzons, A. D.; Cunningham, V. L. Green Chem.
2002, 4, 521–527. doi:10.1039/B206169B
45.SDBS Web; National Institute of Advanced Industrial Science and
Technology, 2015, http://sdbs.db.aist.go.jp.
46.Horton, D.; Lauterback, J. H. J. Org. Chem. 1969, 34, 86–92.
doi:10.1021/jo00838a021
47.Shull, B. K.; Wu, Z.; Koreeda, M. J. Carbohydr. Chem. 1996, 15,
955–964. doi:10.1080/07328309608005701
2233