Synthesis of carnitine benzyl esters as prodrugs

Article abstract of DOI:10.3184/030823408X324689

The introduction of C-2 acyl groups and a benzyl ester onto L-carnitine generated a series of carnitine benzyl esters as prodrug with improved liposolubility, stability and bioavailability.

Full text of DOI:10.3184/030823408X324689

JOURNAL OF CHEMICAL RESEARCH 2008
JUNE, 327–330
RESEARCH PAPER 327
Synthesis of carnitine benzyl esters as prodrugs
Xiao-wei Gonga, Jin-pei Lib, Ji-feng Wuc, Xun Li a*, Hai-min Zhaid, Bo Fengd, Wen-fang Xua*
and Wei Tanga,e
aCollege of Pharmacy, Shandong University, Ji’nan 250012, P.R. China
bLiaocheng People’s Hospital, 252000, P.R. China
cJi’nan Public Security, Shandong, 250000, P.R. China
dQidu Pharmaceutical Co. LTD, Zibo, 255400, P.R. China
eHepato-Biliary-Pancreatic Surgery Division, Department of Surgery, Graduate School of Medicine, the University of Tokyo,
Tokyo 113-8655, Japan
The introduction of C-2 acyl groups and a benzyl ester onto L-carnitine generated a series of carnitine benzyl esters
as prodrug with improved liposolubility, stability and bioavailability.
Keywords: carnitine benzyl esters, prodrug, synthesis, neuroprotective
Carnitine (4-N-trimethylammonium-3-hydroxybutyric acid),
an essential amino acid-like inner salt, is widespread in the
tissues of animals, plants and microorganisms.1 Of its two
optically active enantiomers (D and L), only L-carnitine (LC,
Fig. 1), a natural occurring betaine with vitamin properties, has
attracted considerable attention in recent years. It is non-toxic,
non-mutagenic, and has almost no skin irritation properties.2
It also plays important role in improving myocardial function,
pregnancy rate and spermatogenesis in patients affected by
male infertility.3
R
OH
O
N+
O
O
N+
COO-
R'
O
(L)-carnitine 1
hydroxyl- and carboxyl-based
carnitine derivatives
Fig. 1 Chemical structures of L-carnitine 1 and its derivatives.
Another interesting property of L-carnitine is its
bioavailability based on its transport across membranes via
some carnitine transporters, e.g. OCTN1, OCTN2, OCTN3,
CT2, etc. and the amino acid transporter ATB0,+, which can
recognise neutral as well as cationic amino acids based on the
quaternary amine of carnitine.4 These transporters, mostly
found in peripheral tissues, are responsible for the high-
affinity uptake of carnitine across the plasma membrane,
and also transport carnitine in other specialised tissues such
as sperm.5 This characteristic makes carnitine particularly
useful for the transport of drugs directly to the site where they
can exert their pharmacological activity, preventing the drug
being metabolised by the liver.6
Because of the importance of L-carnitine in pharmaceutical
sciences, a number of synthetic derivatives of L-carnitine
have been developed with improved therapeutically function
or effect over carnitine itself. They are mainly hydroxyl- and/
or carboxyl-based derivatives (Fig. 1).7-9 Nevertheless, these
water-soluble quaternary ammonium salts are extremely
hydrophilic. The hydroxyl-based carnitine esters do not have
a significant improvement in liposolubility,10 which is a
disadvantage for pharmaceutical preparations. Only capsules,
tablets and freeze-dried powder injections, have appeared on
the market as drugs at present.11 This increases the potential
for designing a wide variety of carboxyl-based carnitine
prodrugs that can utilise ATB0,+ as drug delivery system.
To obtain improved oral bioavailability via introduction of
hydrophobic esters, the benzyl ester was selected owing to its
solution-stable and biolabile properties.12,13 Thus, our efforts in
developingL-carnitinederivativesasappropriatepharmaceuticals
led us to synthesise a series of novel benzyl carnitine esters
(4a–4j), serving as potential prodrug of carnitine.
the acid chloride with oxalyl chloride and and coupled with
benzyl alcohol to give target compounds 4a–j. The 1H NMR,
IR and high resolution mass spectra data for the final products
are in good agreement with the title compound and exhibit no
discernible impurities.
Results and discussion
The synthetic methods for preparing carnitine derivatives
include ion exchange resin,14 1-iodooctadecane/DMF-
dioxane,15 condensation reaction by using dicyclohexy-
carbodiimmide (DCC) and 4-(dimethylammino)pyridine
(DMAP),8 and 1-bromo-1-chloroethene method.16 However,
these methods almost involve tedious work-up process for
the final products, which is unsatisfactory for commercial
production. Our improved work-up is relatively simple by
using appropriate recrystallisation solvents with good yields.
Studies have shown over several decades that L-carnitine
and its derivatives may play a role in neuroprotection
and neurotransmission.17 Hence, compounds 4a–j were
evaluated for their neuroprotective effect in vitro by 3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
colourimetric assay on CoCl2-induced apoptosis in PC12 cell
line (pheochromocytoma), and the results were summarised
in Table 1. Parallel experiments for the corresponding
debenzylated compounds 2a–j were also conducted.
The OD630 values were calculated as the ratio of the IC50
in the presence or absence of carnitine derivatives (10 mg/l)
before addition of CoCl2 (300 μM), using a reference
wavelength of 630 nm and a test wavelength of 570 nm.
All the data are mean ± SD of three independent experiments.
From Table 1, we can see that almost all the tested carnitine
benzyl esters (4a–j) could block CoCl2-induced apoptosis in
PC12 cells.18 The results indicated, that the newly synthesised
carnitine derivatives have a neuroprotective activity. More
importantly, with the alteration of their physicochemical
properties, they may prolong their effective time and will be
devoid of side effects, through increasing the liposolubility,
stability and bioavailability. They may be used as potential
prodrugs.
The synthetic route is summarised in Scheme 1. Briefly,
the acyl chorides 1 of different carboxylic acids, were reacted
with the commercial available L-carnitine in the presence
of trifluoroacetic acid (TFA) at 40–50°C to generate acyl
carnitine derivatives 2. The carboxyl then was converted to
* Correspondent. E-mail: tjulx2004@sdu.edu.cn

328 JOURNAL OF CHEMICAL RESEARCH 2008
O
O
SOCl2
R
R
Cl
(1)
R
OH
reflux
O
O
O
CF3COOH
OC
OH
OH
O
Cl-
H3C
N+
OH
CH3
Cl-
N+
CH3
H3C
CH3
CH3
(2)
O
R
R
OH
OC
Cl
O
O
O
Cl
O
N+
O
·HCl
O
O
Cl
Cl-
H3C
DMSO,
O
OC
CH2Cl2
N+
CH3
CH3
(3)
(4)
Scheme 1
Table 1 Effect of derivatives of 2a–j and 4a–j on the PC12 cells viability induced by CoCl2
R
R
O
O
O
O
N+
O
·HCl
O
OH
Cl-
H3C
N+
O
CH3
CH3
Acyl carnitine benzyl ester
4
Acyl carnitine 2
Entry
R
M.p./°C
Yield/%
OD630
(acyl carnitine 2)
OD630 (carnitine
benzoate ester 4)
Control
1
1
CoCl2
(alone)
4a
0.4589
0.4696
0.4589
0.4630
180.5~183.0
58
4b
4c
4d
4e
4f
CH3
146.0~148.0
108.0~110.5
112.0~114.0
134.0~136.0
136.0~138.0
117.5~120.0
129.5~131.0
115.5~118.0
65.0~67.0
68
71
66
69
70
74
73
62
52
0.5574
0.6039
0.7143
0.7026
0.7186
0.7339
0.5030
0.5342
0.5226
0.5602
0.6054
0.7042
0.7027
0.7185
0.7355
0.4959
0.5467
0.5153
CH2CH3
CH2CH2CH3
CH2CH(CH3)2
CH2CH2CH2CH3
CH2CH2CH(CH3)2
CH2CH2CH2CH2CH3
CH2(CH2)5CH3
(CH2)7CH=CH(CH2)7CH3
4g
4h
4i
4j
*P<0.05; **P<0.01 vs negative control (300 µM CoCl2 alone).
plates) and visualised with iodine. All commercially available
compounds were directly used without further purification. Yields
refer to isolated products after purification. Melting points were
determined with capillary apparatus and uncorrected. IR spectra
were recorded in the range of 4000–600 cm-1 using a Nicolet
It is likely that the esters will be converted to biologically
active carboxylic acid. Hence their the metabolic stability
and effective blood drug levels might be improved. The
corresponding experimental evaluation is underway, and the
results will be reported in the near future.
1
Nexus 470FT-Spectrometer with KBr disks. H NMR spectra was
determined in D2O on a Bruker 400 MHz spectrometer with TMS
as an internal standard. Electrospray ionisation mass spectrometry
(ESI–MS) was performed on an API 4000 spectrometer. Elemental
analyses were carried out on an Elementar Elvario III C, H, and N
elemental analyser.
Conclusion
In conclusion, novel carnitine benzyl esters were prepared
by acylation and esterification using L-carnitine and
different substituted carboxylic acids as starting materials.
The neuroprotective effect of final compounds (4a–j) and
their corresponding debenzylated compounds (2a–j) in vitro
showed that they may be potential prodrugs with improved
neuroprotective effect.
General procedure for the preparation of compounds 4a–j
A mixture of the carboxylic acid (1 mol) and thionyl chloride
(4.2 mol) was stirred under reflux until the disappearance of the
starting materials as evidenced by TLC (about 4 h). After reaction,
the excess thionyl chloride was removed in vacuum, and the yellow
oily product 1 was directly used in the following reaction without any
purification.
Experimental
The course of the reaction and products were routinely monitored
by thin-layer chromatography (TLC) on silica gel (precoated GF254
L-Carnitine hydrochloride (30.06 g, 0.125 mol) was dissolved in
anhydrous trifluoroacetic acid 100 ml, followed by the dissolution of

JOURNAL OF CHEMICAL RESEARCH 2008 329
the above compound 1 in an ice bath. The resulting mixture was stirred
under 45–50°C until the starting material disappeared as shown by
TLC (about 20 h). After the reaction was completed, the solvent was
removed in vacuo and acetone 400 ml was added. After stirring for
another 2 h, the white precipitate was removed, and then diethyl ether
800 ml was added to the filtrate. The resultant mixture was cooled
to room temperature and filtered to give the white precipitate which
was then collected and recrystallised from ethanol–diethyl ether
(V:V = 1:4) to give compounds 2a–j as colourless needles.
Compound 2 (0.1 mol) was dissolved in of dichloromethane
100 ml, below 0°C and freshly distilled oxalyl chloride (15 ml,
0.12 mol) was added dropwise. The resulting mixture was reacted at
45–50°C until the reaction was complete. The solvent was removed
in vacuo and the white residue was dissolved in of anhydrous dimethyl
sulfoxide (DMSO) 100 ml followed by the addition of benzyl alcohol
(0.18 mol) at room temperature. The resulting mixture reacted at
50°C until the disappearance of starting materials as evidenced by
TLC. After adding diethyl ether(80 ml) and stirring for 2 h, the white
precipitate was collected and dried in vacuo below 40°C. The crude
product was recrystallised by the mixture of ethyl acetate/diethyl
ether (V:V = 1:2, 75 ml) to give the target compounds 4a–j.
1173 (nC-N), 616, 700, 753, 936 (aromatic ring); ESI–MS (m/z): 337.4
[M + H]+. Calcd. for C19H30ClNO4: C, 61.4; H, 8.1; N, 3.8. Found: C,
61.3; H, 8.3; N, 3.7%.
(R)-4-(benzyloxy)-N,N,N-trimethyl-2-(3-methylbutanoyloxy)-4-
oxobutan-1-ammonium chloride (4g): M.p. 117.5–120.0°C; 1H NMR d
0.78–0.81(3H, d, J = 6.6 Hz, (CH3)2CH–), 0.85–0.87 (3H, d, J = 6.6 Hz,
(CH3)2CH–), 2.15–2.19(1H, m, (CH3)2CH–), 2.77–2.84 (2H, m,
–CH2COOCH–), 3.10–3.15 (2H, m, –CH2COOCH2–), 3.07 (9H, s,
(CH3)3N–), 3.56–3.76 (2H, dd, J = 10.2, 14.4 Hz, –NCH2–), 5.11 (2H, s,
–CH2C6H5), 5.59 (1H, m, –NCH2CH–), 7.34–7.38 (5H, m, –CH2C6H5).
IR cm-1 (KBr plate): 3020, 2957 (gCH), 1736, 1704 (gC=O), 1488, 1412
(dCH2,CH3), 1181 (nC-N), 665, 699, 752, 880, 938 (aromatic ring); ESI–
MS (m/z): 336.5 [M + H]+. Calcd. for C19H30ClNO4: C, 61.4; H, 8.1; N,
3.8. Found: C, 61.3; H, 8.2; N, 3.6%.
(R)-4-(benzyloxy)-2-(hexanoyloxy)-N,N,N-trimethyl-4-oxobutan-1-
1
ammonium chloride (4h): M.p. 129.5–131.0°C; H NMR d 0.62–0.64
(3H, m, CH3CH2–), 0.96–1.02 (4H, m, –CH3CH2CH2–), 1.98–2.07
(2H, m, –CH2CH2COO–), 2.53–2.62 (2H, m, –CH2CH2COO–), 3.07–
3.12 (2H, m, –CHCH2COO–), 3.04 (9H, s, (CH3)3N–), 3.56 (2H, m,
–NCH2–), 4.90 (2H, s, –CH2C6H5), 5.50–5.57 (1H, m, –NCH2CH–),
7.29–7.31 (5H, m, –CH2C6H5); IR cm-1 (KBr plate): 3014, 2957
(gCH), 1734 (gC=O), 1480, 1413 (dCH2,CH3), 1174 (nC-N), 700, 727, 768,
935 (aromatic ring); ESI–MS (m/z): 350.4 [M + H]+. Anal. Calcd. for
C20H32ClNO4: C, 62.3; H, 8.4; N, 3.6. Found: C, 62.3; H, 8.4; N, 3.6%.
(R)-4-(benzyloxy)-N,N,N-trimethyl-2-(octanoyloxy)-4-oxobutan-1-
ammonium chloride (4i): M.p. 115.5–118.0°C; 1H NMR d 0.76–0.78
(3H, t, CH3CH2–), 1.08–1.24 (8H, m, –CH3(CH2)2–), 2.35–2.40 (2H,
m, –CH2CH2COO–), 2.75–2.78 (2H, m, –CH2CH2COO–), 3.10–3.16
(2H, m, –CHCH2COO–), 3.13 (9H, s, (CH3)3N–), 3.60 (2H, dd,
J = 8.7, 14.4 Hz, –NCH2–), 5.08 (2H, s, –CH2C6H5), 5.57–5.63
(1H, m, –NCH2CH–), 7.33–7.39 (5H, m, –CH2C6H5); IR cm-1 (KBr
plate): 3017, 2927 (gCH), 1735, 1698 (gC=O), 1646 (gC=C), 1482, 1416
(dCH2,CH3), 1174 (nC-N), 666, 726, 880, 938 (aromatic ring); ESI–MS
(m/z): 378.6 [M + H]+. Anal. Calcd. for C22H36ClNO4: C, 63.8; H,
8.8; N, 3.4. Found: C, 63.8; H, 6.8; N, 3.3%.
(E)-4-(benzyloxy)-2-(cinnamoyloxy)-N,N,N-trimethyl-4-oxobutan-
1
1-ammonium chloride (4a): M.p. 180.5–183.0°C; H NMR d 2.71–
2.76 (2H, m, –CH2COO–), 2.98 (9H, s, (CH3)3N–), 3.58 (2H, d,
J = 6.9 Hz, –NCH2–), 4.79 (2H, s, –CH2C6H5), 5.60 (1H, m,
–NCH2CH–), 6.05 (1H, d, J = 15.9 Hz, –CH=CHCOO–), 6.05 (1H,
d, J = 15.9 Hz, –CH=CHCOO–), 6.84–7.00 (5H, m, –CH2C6H5),
7.10–7.4 (5H, m, –CH=CHC6H5); IR cm-1 (KBr plate): 3067, 3027
(gCH), 1729, 1695 (gC=O), 1669, 1628 (gC=C), 1504, 1588 (gAr–C), 1486,
1431 (dCH2,CH3), 1208 (nC–N), 681, 695, 723, 758, 917 (aromatic ring);
ESI–MS (m/z): 436.2 [M + H]+. Anal. Calcd. for C23H28ClNO4: C,
66.1; H, 6.8; N, 3.4. Found: C, 65.9; H, 6.9; N, 3.4%.
(R)-2-acetoxy-4-(benzyloxy)-N,N,N-trimethyl-4-oxobutan-1-
ammonium chloride (4b): M.p. 146.0–148.0°C; 1H NMR d 2.01
(3H, s, CH3COO–), 2.62–2.65 (2H, m, –CH2COO–), 3.12 (9H, s,
(CH3)3N–), 3.58 (2H, m, –NCH2–), 4.56 (2H, s, –CH2C6H5), 5.53
(1H, m, –NCH2CH–), 7.35–7.39 (5H, m, –CH2C6H5); IR cm-1 (KBr
plate): 3013 (gCH), 1733 (gC=O) 1478, 1411 (dCH2,CH3), 1215 (nC–N),
709, 726, 768, 934 (aromatic ring); ESI–MS (m/z): 294.4 [M + H]+.
Anal. Calcd. for C16H24ClNO4: C, 58.3; H, 7.3; N, 4.3. Found: C,
58.3; H, 7.3; N, 4.3%.
(R,E)-4-(benzyloxy)-N,N,N-trimethyl-2-(octadec-9-enoyloxy)-
4-oxobutan-1-ammonium chloride (4j): M.p. 65.0–67.0°C;
1H NMR d 0.86–0.90 (3H, t, CH3CH2–), 1.18–1.42 (20H, m,
–(CH2)6CH2CHCHCH2(CH2)4), 1.68 (4H, m, –CH2CHCHCH2–),
2.22–2.29 (2H, m, –CH2CH2COO–), 2.75–2.80 (2H, m,
–CH2CH2COO–), 3.03–3.10 (2H, m, –CHCH2COO–), 3.24 (9H, s,
(CH3)3N–), 3.87 (2H, m, –NCH2–), 5.10 (2H, s, –CH2C6H5), 5.51–5.62
(1H, m, –NCH2CH–), 6.43 (1H, d, J = 14.7 Hz, –CH=CH–), 6.87 (1H,
d, J = 12.5 Hz, –CH=CH–), 7.27–7.36 (5H, m, –CH2C6H5); IR cm-1
(KBr plate): 3034, 3028 (gCH), 1735, 1688 (gC=O), 1479, 1468
(dCH2,CH3), 1184 (nC-N), 705, 712, 753, 799, 914 (aromatic ring); ESI–
MS (m/z): 552.7 [M + H]+. Anal. Calcd. for C32H54ClNO4: C, 69.6; H,
9.9; N, 2.5. Found: C, 69.6; H, 9.9; N, 2.6%.
(R)-4-(benzyloxy)-N,N,N-trimethyl-4-oxo-2-(propionyloxy)butan-
1
1-ammonium chloride (4c): M.p. 108.0–110.5°C; H NMR d 1.00–
1.05 (3H, t, CH3CH2COO–), 2.51–2.58 (2H, m, –CH3CH2COO–),
3.03–3.08 (2H, m, –CH2COO–), 3.19 (9H, s, (CH3)3N–), 3.58 (2H,
dd, J = 8.4, 12.8 Hz, –NCH2–), 4.49 (2H, s, –CH2C6H5), 5.01 (1H,
m, –NCH2CH–), 7.25–7.30 (5H, d, J = 2.8 Hz, –CH2C6H5); IR cm-1
(KBr plate): 3061, 2926 (gCH), 1725 (gC=O), 1479, 1403 (dCH2,CH3),
1177 (nC-N), 727, 768, 876, 933 (aromatic ring), ESI–MS (m/z): 308.7
[M + H]+. Anal. Calcd. for C17H26ClNO4: C, 59.4; H, 7.6; N, 4.1.
Found: C, 59.5; H, 7.7; N, 4.0%.
Data for 2a–j
(R,E)-3-carboxy-2-(cinnamoyloxy)-N,N,N-trimethylpropan-1-
ammonium chloride (2a): M.p. 206.0–208.0; 1H NMR d 2.70–2.72(2H,
m, –CH2COO–), 3.03 (9H, s, (CH3)3N–), 3.54 (2H, m, –NCH2–), 5.57
(1H, m, –NCH2CH–), 6.30 (1H, d, J = 15.9 Hz, –CH=CHCOO–),
(R)-4-(benzyloxy)-2-(butyryloxy)-N,N,N-trimethyl-4-oxobutan-1-
ammonium chloride (4d): M.p. 112.0–114.0°C; 1H NMR d 0.75–0.81
(3H, t, CH3CH2–), 1.40–1.47 (2H, m, –CH3CH2–), 2.18–2.22 (2H,
m, –CH2CH2COO–), 3.14–3.27 (2H, m, –CHCH2COO–), 3.05 (9H,
s, (CH3)3N–), 3.58 (2H, dd, J = 8.4, 12.8 Hz, –NCH2–), 5.10 (2H, s,
–CH2C6H5), 5.57 (1H, m, –NCH2CH–), 7.31–7.37 (5H, d, –CH2C6H5);
IR cm-1 (KBr plate): 2966(gCH), 1739 (gC=O), 1690 (gC=C), 1504, 1588
(gAr-C), 1483, 1456 (dCH2,CH3), 1173 (nC-N), 681, 699, 752, 968 (aromatic
ring); ESI–MS (m/z): 322.4 [M + H]+. Calcd. for C18H28ClNO4: C,
60.4; H, 7.9; N, 3.9. Found: C, 60.5; H, 7.8; N, 3.9%.
7.24–7.42 (5H, m, –CH2C6H5), 7.53 (1H, d, J
= 15.9 Hz,
–CH=CHCOO–). IR cm-1 (KBr plate): 2500–3000 (gOH), 1729, 1701
(gC=O), 1637, 1577 (gC=C), 1486, 1450 (dCH2,CH3), 1196 (nC-N), 712,
768 (aromatic ring). ESI–MS (m/z): 292.4 [M + H]+. Anal. Calcd. for
C16H22ClNO4: C, 58.6; H, 6.8; N, 4.3 Found: C, 58.7; H, 6.8; N, 4.2%.
These analytical data were agreement with the literature.19
(R)-2-acetoxy-3-carboxy-N,N,N-trimethylpropan-1-ammonium
chloride (2b): M.p. 187.0–189.0. The analytical data were shown in
literature.20
(R)-4-(benzyloxy)-2-(isobutyryloxy)-N,N,N-trimethyl-4-oxobutan-
1
1-ammonium chloride (4e): M.p. 134.0–136.0°C; H NMR d 0.97–
1.09 (6H, m, (CH3)2CH–), 2.46–2.51 (1H, m, (CH3)2CH–), 2.75–
2.78 (2H, m, –CH2COO–), 2.83 (9H, s, (CH3)3N–), 3.56 (2H, dd,
J = 3.6, 14.4 Hz, –NCH2–), 5.12 (2H, s, –CH2C6H5), 5.59 (1H, m,
–NCH2CH–), 7.32–7.38 (5H, m, –CH2C6H5); IR cm-1 (KBr plate):
3229, 2971 (gCH), 1732 (gC=O), 1480, 1391 (dCH2,CH3), 1179 (nC-N),
700, 718, 755, 799, 935 (aromatic ring); ESI–MS (m/z): 422.6 [M +
H]+. Calcd. for C18H28ClNO4: C, 60.4; H, 7.9; N, 3.9. Found: C, 60.3;
H, 7.9; N, 3.9%.
(R)-3-carboxy-N,N,N-trimethyl-2-(propionyloxy)propan-1-
ammonium chloride (2c): M.p. 161.0–163.0. The analytical data were
agreement with literature.21
(R)-2-(butyryloxy)-3-carboxy-N,N,N-trimethylpropan-1-ammonium
chloride (2d): M.p. 159.0–162.0; 1H NMR d 0.81 (3H, d, J = 14.7 Hz,
CH3CH2–), 1.48–1.60 (2H, m, –CH3CH2–), 2.32–2.37 (2H, m,
–CH2CH2COO–),2.75(2H,m,–CHCH2COO–),3.12(9H,s,(CH3)3N–),
3.58 (2H, m, –NCH2–), 5.57 (1H, m, –NCH2CH–). IR cm-1 (KBr plate):
2500–3000 (gOH), 1735 (gC=O), 1479, 1413 (dCH2,CH3), 1175 (nC-N).
ESI–MS (m/z): 232.4 [M + H]+. Anal. Calcd. for C11H22ClNO4: C,
49.4; H, 8.3; N, 5.2. Found: C, 49.5; H, 8.3, N, 5.1%.
(R)-4-(benzyloxy)-N,N,N-trimethyl-4-oxo-2-(pentanoyloxy)butan-
1
1-ammonium chloride (4f): M.p. 136.0–138.0°C; H NMR d 0.77–
0.80 (3H, t, CH3CH2–), 0.88–0.93 (2H, m, –CH3CH2–), 1.45–1.47
(2H, m, –CH2CH2CH2–), 2.54–2.62 (2H, m, –CH2CH2COO–),
3.04–3.07 (2H, m, –CHCH2COO–), 3.13 (9H, s, (CH3)3N–), 3.58
(2H, dd, J = 2.8, 10.2 Hz, –NCH2–), 5.08 (2H, s, –CH2C6H5), 5.55
(1H, m, –NCH2CH–), 7.34 (5H, d, J = 8.4 Hz, –CH2C6H5); IR cm-1
(KBr plate): 3020, 2959 (gCH), 1732 (gC=O), 1480, 1455 (dCH2,CH3),
(R)-3-carboxy-N,N,N-trimethyl-2-(3-methylbutanoyloxy)propan-1-
1
ammonium chloride (2e): M.p. 160.0–162.5; H NMR d 1.06 (6H,
dd, J = 2.4, 7.2 Hz, (CH3)2CH–), 2.55–2.65 (1H, m, (CH3)2CH–),
2.74 (2H, d, J = 6.3 Hz, –CH2COO–), 3.12 (9H, s, (CH3)3N–),
3.59–3.90 (2H, m, –NCH2–), 5.57–5.64 (1H, m, –NCH2CH–).

330 JOURNAL OF CHEMICAL RESEARCH 2008
IR cm-1 (KBr plate): 2500–3000 (gOH), 1734, 1701 (gC=O), 1479, 1443
(dCH2,CH3), 1186 (nC-N). ESI–MS (m/z): 232.4 [M + H]+. Anal. Calcd.
for C11H22ClNO4: C, 49.4; H, 8.3; N, 5.2. Found: C, 49.3; H, 8.4; N,
5.2%.
We are thankful for financial support from the Natural Science
Foundation of China (Grant Nos. 30701053; 30772654), and
the Doctoral Youth Foundation of Ministry of Education
of China (No 20070422061). In addition, this work was
supported in part by Grants-in-Aid from the Ministry of
Education, Science, Sports and Culture of Japan.
(R)-3-carboxy-N,N,N-trimethyl-2-(pentanoyloxy)propan-1-
1
ammonium chloride (2f): M.p. 146.0–148.0; H NMR d 0.78 (3H, t,
J = 14.7 Hz, CH3CH2–), 1.18–1.30 (2H, m, –CH3CH2–), 1.46–1.56 (2H,
m, –CH2CH2CH2–), 2.35 (2H, t, J = 15.3 Hz, –CH2CH2COO–), 2.75
(2H, d, J = 6.3 Hz, –CHCH2COO–), 3.12 (9H, s, (CH3)3N–), 3.59–3.88
(2H, m, –NCH2–), 5.57–5.64 (1H, m, –NCH2CH–). IR cm-1 (KBr plate):
2500–3000 (gOH), 1736 (gC=O), 1480, 1412 (dCH2,CH3), 1170 (nC-N).
ESI–MS (m/z): 246.5 [M + H]+. Anal. Calcd. for C12H24ClNO4: C,
51.2; H, 8.6; N, 5.0. Found: C, 51.1; H, 8.6; N, 4.9%.
Received 30 January 2008; accepted 10 May 2008
Paper 08/5077 doi: 10.3184/030823408X324689
References
1
2
3
4
5
6
7
I.B. Fritz, Current Concepts in Carnitine Research, ed. A.L. Carter CRC
Press, Boca Raton, FL, 1992, pp. 107.
B. Kamm, M. Kamm, A. Kiener and H.P. Meyer, Appl. Microbiol.
Biotechnol., 2005, 67, 1.
X. Zhou, F. Liu and S. Zhai, Asia Pac. J. Clin. Nutr., 2007, 16 Suppl,
383.
K.A. NaBcz, D. Miecz, V. Berezowski and R. Cecchelli, Mol. Aspects
Med., 2004, 25, 551.
W. Xuan, A.M. Lamhonwah, C. Librach, K. Jarvi, and I. Tein, Biochem.
Biophys. Res. Commun., 2003, 306, 121.
A.P. Aprilia, M.O.T. Roma, M.S. Nettuno, L.C. Pomezia and G.S. Rome,
2004, US 6797281B1.
S.R. Srinivas, P.D. Prasad, N.S. Umapathy, V. Ganapathy and
P.S. Shekhawat, Am. J. Physiol. Gastrointest. Liver Physiol., 2007, 293,
G1046.
(R)-3-carboxy-N,N,N-trimethyl-2-(4-methylpentanoyloxy)propan-
1-ammonium chloride (2g): M.p. 166.0–168.0; 1H NMR d 0.85
(6H, d, J = 6.6 Hz, (CH3)2CH–), 2.91–2.04 (1H, m, (CH3)2CH–),
2.24 (2H, t, J = 12.9 Hz, –CH2COOCH–), 2.77 (2H, d, J = 6.0 Hz,
–CH2COOCH2–), 3.13 (9H, s, (CH3)3N–), 3.60–3.89 (2H, m,
–NCH2–), 5.57–5.64 (1H, m, –NCH2CH–). IR cm-1 (KBr plate): 2500–
3000 (gOH), 1736, 1715 (gC=O), 1484, 1412 (dCH2,CH3), 1182 (nC-N).
ESI–MS (m/z): 246.5 [M + H]+. Anal. Calcd. for C12H24ClNO4: C,
51.2; H, 8.6; N, 5.0. Found: C, 51.5; H, 8.6; N, 4.9%.
(R)-3-carboxy-2-(hexanoyloxy)-N,N,N-trimethylpropan-1-
1
ammonium chloride (2h): M.p. 170.0–172.0; H NMR d 0.76 (3H,
t, J = 13.8 Hz, CH3CH2–), 1.18–1.23 (4H, m, –CH3CH2CH2–),
1.48–1.58 (2H, m, –CH2CH2COO–), 2.35 (2H, t, J = 15.3 Hz,
–CH2CH2COO–), 2.75 (2H, d, J = 6.0 Hz, –CHCH2COO–), 3.12
(9H, s, (CH3)3N–), 3.59–3.89 (2H, m, –NCH2–), 5.57–5.63 (1H, m,
–NCH2CH–). IR cm-1 (KBr plate): 2500–3000 (gOH), 1736 (gC=O),
1480, 1415 (dCH2,CH3), 1170 (nC-N). ESI–MS (m/z): 260.5 [M + H]+.
Anal. Calcd. for C13H26ClNO4: C, 52.8; H, 8.9; N, 4.7. Found: C,
52.8; H, 8.9, N, 4.7%.
8
9
O. Piermatti, F. Fringuelli, L. Pochini, C. Indiveri and C.A. Palmerini,
Bioorg. Med. Chem., 2008, 16, 1444.
E.J. Tadeusiak, Bioorg. Chem., 2004, 32, 473.
10 A. Inano, Y. Sai, H. Nikaido, N. Hasimoto, M. Asano, A. Tsuji and
I. Tamai, Biopharm. Drug Dispos., 2003, 24, 357.
11 Index by database: MICROMEDEX(R) Healthcare Series Vol. 121. (or
Thomson micromedex Vol.121)
(R)-3-carboxy-N,N,N-trimethyl-2-(octanoyloxy)propan-1-
12 T. Kawaguchi, T. Hasegawa, T. Seki, K. Juni, Y. Morimoto, A. Miyakawa
and M. Saneyoshi, (DDI): Chem. Pharm. Bull. (Tokyo)., 1992, 40, 1338.
13 H. Bundgaard, E. Jensen and E. Falch, Pharm. Res., 1991, 8, 1087.
14 C. Cavazza and M.O. Tinti, Esters of alkoxy–acyl derivatives of carnitine
and pharmaceutical compositions containing same. 1985, US 4,551,477.
15 M. Calvani, L. Critelli, G. Gallo, F. Giorgi, G. Gramiccioli, M. Santaniello,
N. Scafetta, M.O. Tinti and F. De Angelis, J. Med. Chem., 1998, 41,
2227.
16 C. Pisano, M.O. Tinti, M. Santaniello, L. Critelli and G. Salvatori, Esters
of L–carnitine or alkanoyl L–carnitine. 2004, US 6,797,281 B1.
17 A. Virmani, F. Gaetani and Z. Binienda, Ann. NY Acad. Sci., 2005, 1053,
183.
18 J.Y. Jung, H.C. Mo, K.H. Yang, Y.J. Jeong, H.G. Yoo, N.K. Choi,
W.M. Oh, H.K. Oh, S.H. Kim, J.H. Lee, H.J. Kim and W.J. Kim, Life Sci.,
2007, 80, 1355.
19 de W. Paolo, Novel acyl–derivatives of cartine and process for their
preparation. 1980, UK GB 2,028,826 A.
1
ammonium chloride (2i): M.p. 172.0–174.0; H NMR d 0.76 (3H, t,
J = 13.5 Hz, CH3CH2–), 1.19–1.21 (8H, m, –CH3(CH2)2–), 1.51–1.56
(2H, m, –CH2CH2COO–), 2.35–2.40 (2H, m, –CH2CH2COO–), 2.75
(2H, d, J = 6.0 Hz, –CHCH2COO–), 3.12 (9H, s, (CH3)3N–), 3.60–
3.89 (2H, m, –NCH2–), 5.57–5.63 (1H, m, –NCH2CH–). IR cm-1 (KBr
plate): 2500–3000 (gOH), 1735, 1716 (gC=O), 1484, 1416 (dCH2,CH3), 1174
(nC-N). ESI–MS (m/z): 288.4 [M + H]+. Anal. Calcd. for C15H30ClNO4:
C, 55.6; H, 9.3; N, 4.3. Found: C, 55.7; H, 9.4, N, 4.3%.
(R,E)-3-carboxy-N,N,N-trimethyl-2-(octadec-9-enoyloxy)propan-
1
1-ammonium chloride (2j): M.p. 121.0–124.0; H NMR d 0.81 (3H, t,
J = 6.9 Hz, CH3CH2–), 1.12–1.18 (20H, m, –(CH2)6CH2CHCHCH2
(CH2)4), 1.50–1.52 (4H, m, –CH2CHCHCH2–), 2.10–2.14 (2H, m,
–CH2CH2COO–), 2.56 (2H, t, J = 12.6 Hz, –CH2CH2COO–), 3.08–
3.13 (2H, m, –CHCH2COO–), 3.10 (9H, s, (CH3)3N–), 3.60 (2H,
m, –NCH2–), 5.51–5.53 (2H, m, –NCH2CH–), 5.53–5.63 (1H, m,
–NCH2CH–). IR cm-1 (KBr plate): 2500–3000 (gCH), 1716 (gC=O),
1482, 1396 (dCH2,CH3), 1183 (nC-N). ESI–MS (m/z): 426.6 [M + H]+.
Anal. Calcd. for C25H48ClNO4: C, 65.0; H, 10.5; N, 3.0. Found: C,
65.0; H, 10.5; N, 3.0%.
20 H.P. Weber, R.C. Anderson, M. Shapiro, E.B. Villhauer and T. Gullion,
Acta. Cryst., 1995, C51, 2570.
21 C. Cavazza, Amides of acyl–carnitines, process for preparing same and
pharmaceutical compositions containing such amides. 1980, UK GB
2,048,268 A.