Formal synthesis of (-)-pereniporin B and (-)-cinnamosmolide

Article abstract of DOI:10.1080/14786419.2014.930860

The paper describes a new pathway for an efficient synthesis of natural and bioactive drimanic compounds (-)-pereniporin B (1) and (-)-cinnamosmolide (2) from ketodiol 7, an intermediate obtained before from accessible labdane diterpenoid (+)-larixol (3). The key step involves allylic bromination of acetate 8 with N-bromosuccinimide. The in vitro antimicrobial and antifungal activities of all compounds are also reported. Their structures were confirmed by both spectroscopic data and chemical transformations.

Full text of DOI:10.1080/14786419.2014.930860

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Formal synthesis of ( - )-pereniporin B
and ( - )-cinnamosmolide
ab
a
a
Alexandru Ciocarlan , Aculina Aricu , Nicon Ungur , Andrei
a
a
bc
bc
Biriiac , Mihai Coltsa , Alina Nicolescu , Calin Deleanu
&
d
Nicoleta Vornicu
a
Institute of Chemistry, Academy of Sciences of Moldova,
Academiei Street 3, MD-2028 Chisinau, Republic of Moldova
b
‘Petru Poni’ Institute of Macromolecular Chemistry of the
Romanian Academy, Aleea Grigore Ghica Voda 41A, RO-700487
Iasi, Romania
c
‘Costin D. Nenitescu’ Centre of Organic Chemistry, Romanian
Academy, Splaiul Independentei 202B, P.O. Box 35-98, RO-060023
Bucharest, Romania
d
Metropolitan Center of Research T.A.B.O.R., Closca 9,
RO-700066 Iasi, Romania
Published online: 27 Jun 2014.
To cite this article: Alexandru Ciocarlan, Aculina Aricu, Nicon Ungur, Andrei Biriiac, Mihai Coltsa,
Alina Nicolescu, Calin Deleanu & Nicoleta Vornicu (2014): Formal synthesis of ( - )-pereniporin
B and ( - )-cinnamosmolide, Natural Product Research: Formerly Natural Product Letters, DOI:
10.1080/14786419.2014.930860
To link to this article: http://dx.doi.org/10.1080/14786419.2014.930860
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Natural Product Research, 2014
http://dx.doi.org/10.1080/14786419.2014.930860
Formal synthesis of (2)-pereniporin B and (2)-cinnamosmolide
ab
Alexandru Ciocarlan *, Aculina Aricu , Nicon Ungur , Andrei Biriiac , Mihai Coltsa ,
a
a
a
a
bc bc
Alina Nicolescu , Calin Deleanu and Nicoleta Vornicu
d
a
Institute of Chemistry, Academy of Sciences of Moldova, Academiei Street 3, MD-2028 Chisinau, Republic
of Moldova; ‘Petru Poni’ Institute of Macromolecular Chemistry of the Romanian Academy, Aleea
b
c
Grigore Ghica Voda 41A, RO-700487 Iasi, Romania; ‘Costin D. Nenitescu’ Centre of Organic Chemistry,
Romanian Academy, Splaiul Independentei 202B, P.O. Box 35-98, RO-060023 Bucharest, Romania;
Metropolitan Center of Research T.A.B.O.R., Closca 9, RO-700066 Iasi, Romania
d
(
Received 29 January 2014; final version received 1 June 2014)
The paper describes a new pathway for an efficient synthesis of natural and bioactive
drimanic compounds (2)-pereniporin B (1) and (2)-cinnamosmolide (2) from
ketodiol 7, an intermediate obtained before from accessible labdane diterpenoid (þ)-
larixol (3). The key step involves allylic bromination of acetate 8 with N-
bromosuccinimide. The in vitro antimicrobial and antifungal activities of all
compounds are also reported. Their structures were confirmed by both spectroscopic
data and chemical transformations.
Keywords: (2)-pereniporin B; (2)-cinnamosmolide; (þ)-larixol; formal synthesis
1
. Introduction
Drimane sesquiterpenoids have a wide range of biological activities (Jansen & de Groot 2004;
Fraga 2013). Drimanic lactone pereniporin B (1) and its acetate cinnamosmolide (2) were
isolated from several species of Canellaceae family: Cinnamosma fragrans (Canonica et al.
1
967), Capsicodendron dinisii (Mahmoud et al. 1980) and Cinnamosma madagascariensis
(
(
(
Harinantenaina et al. 2008), from the culture filtrate of Perenniporia medullaepanis
Basidiomycete) (Kida et al. 1986), and from the stem bark of Warburgia ugandensis
Warburgia) (Rajab & Ndegva 2000), Figure 1.
It has been reported that pereniporin B (1) is a plant growth inhibitor (Kida et al. 1986), while
cinnamosmolide (2) showed in vitro antifungal activity against dermatophites Tricophyton
rubrum, Tricophyton mentagraphytes and Microsporum gypseum (Canonica et al. 1969).
Both metabolites were found to exhibit cytotoxic activity: pereniporin B (1) against friend
leukaemia cells (F5-5) (Morioka et al. 1985) and cinnamosmolide (2) against the 9KB5
carcinoma in cell culture (Mahmoud et al. 1980).
First total syntheses of racemic pereniporin B (1) and cinnamosmolide (2) were performed
in nine steps starting from a drimanic allylic alcohol, with ,5% overall yield (Naito et al.
1
980). Since then several syntheses of 1 in an optically active form have been described,
involving 28 steps (1.8% yield) and (S)-3-hydroxy-2,2-dimethyl-1-cyclohexanone as starting
material (Mori & Takaishi 1989). The enantioselective synthesis of pereniporin B (1) was
performed (Burke et al. 1991) in 19 steps (,3% yield) from an aliphatic vinylsulphoxide.
Another accessible natural diterpenoid zamoranic acid was used for six-step synthesis of
pereniporin B (1) in 11% yield by Urones et al. (1994). The only nine-step synthesis of
*
Corresponding author. Email: algciocarlan@yahoo.com
q 2014 Taylor & Francis

2
A. Ciocarlan et al.
O
O
OH
OR
H
1
2
R = H
R = Ac
Figure 1. (2)-Pereniporin B 1 and (2)-cinnamosmolide 2.
cinnamosmolide (2) was reported in 14% overall yield by transformation of uvidin A
(
Garlaschelli et al. 1991).
Herein we wish to report a new and efficient pathway for the synthesis of (2)-pereniporin B
1) and (2)-cinnamosmolide (2) from (þ)-larixol (3) via key intermediate ketodiol 7. It must be
(
mentioned that previously compound 7 was isolated from natural sources in low amounts (Hayes
et al. 1996; Zhou et al. 2011).
2
. Results and discussion
A valuable intermediate ketodiol 7 was obtained earlier during the synthetic transformation of
uvidin A into (2)-cinnamodial (Garlaschelli & Vidari 1989). The same diol 7 was prepared
during conversion of (þ)-larixol (3) into highly functionalised drimanes (Lagnel et al. 2000).
(
þ)-Larixol (3) can be easily isolated from oleoresin of larch (Larix sp.) and due to hydroxyl
group at C-6 is a suitable starting material for the synthesis of drimanes functionalised at the
same position (Mills 1973). Recently we reported a new synthesis of natural drimanic
compounds (–)-albrassitriol and (–)-6-epi-albrassitriol from (þ)-larixol (3) where ketodiol 7
was obtained in 28.3% overall yield as indicated in Scheme 1 (Vlad et al. 2013).
It is clear that more applications of dienone 7 for the synthesis of drimanes can be developed,
especially when an easy fuctionalisation of the allylic methyl group C-12 can be accomplished.
This has been achieved already by the allylic oxidation with selenium oxide (Garlaschelli
&
Vidari 1989). In our group the same transformation has been carried out using allylic
bromination followed by the substitution of bromide by an acetate group as indicated in
Scheme 2.
The acetylation of the primary hydroxyl group of 7–8 under standard conditions was made
prior to the allylic bromination in order to prevent undesired oxidation at this position. The
allylic bromination of 8 with N-bromosuccinimide (NBS) and subsequent replacement of
bromine by treatment with KOAc gave 10 in high yield (Scheme 2).
OH
OH
OH
O
O
a
b
c
d
H
H
H
H
H
OH
O
O
O
O
3
4
5
6
7
Scheme 1. Synthesis of 6-oxo-7-drimen-9a,11-diol 7 from (þ)-larixol 3. (a) CrO
3
, AcOH, room
temperature, 2 h, 48%; (b) NaOMe, MeOH, room temperature, 24 h, 97%; (c) hn, hexane, N , 58C, 3 h,
2
6
7.5%; (d) OsO , Py, room temperature, 12 h, 90%.
4

Natural Product Research
3
1
1
OR
OAc
OH
OH
OH
O
1
5
OH 12
1
4
9
6
O
f
R
d
OH
e
2
3
10
8
7
OH
5
b
1, 2
H
H
H
H
O
1
4
O
O
O
1
3
1
1
12
7
8
R=H
R=Ac
9 R=Br
10 R=OAc
a
c
Scheme 2. Formal synthesis of pereniporin B 1 and cinnamosmolide 2. (a) Ac
2 h, 86%; (b) NBS, CCl , reflux, 9 h, 91%; (c) KOAc, DMSO, room temperature, 1 h, 98%; (d) K
MeOH, room temperature, 0.5 h, 99%; (e) MnO , CH Cl , room temperature, 70 h, 93%; (f) performed by
2
O, Py, room temperature,
1
4
2
CO
3
,
2
2
2
(
Canonica et al. 1969; Burke et al. 1991).
The acetate groups in 10 were hydrolysed leading to the known triol 11 (Urones et al. 1997;
Zhou et al. 2011), which after oxidation of the least hindered hydroxyl group with MnO2
followed by spontaneous cyclisation and oxidation led to lactone 12 (Kubo et al. 1983). The
transformation of precursor 12 into pereniporin B (1) was reported earlier (Burke et al. 1991). It
includes treatment of lactone 12 with DIBAL-H, followed by Fetizon’s oxidation of the resulted
lactols. Cinnamosmolide (2) can be prepared from pereniporin B (1) by its acetylation under
standard conditions (Canonica et al. 1969).
Compounds 7–12 were screened for their in vitro antifungal and antibacterial activity
against pure cultures of three fungi species (Aspergillus niger, Penicillium frequentans,
Alternaria alternata) and against both Gram-negative (Pseudomonas aeruginosa) and Gram-
positive bacteria (Bacillus polymyxa). According to these assays, bromide 9 exhibited good
antifungal activity with a minimum inhibitory concentration (MIC) value of 0.85 mg/mL in
comparison with the reference compound caspafungin (0.42 mg/mL) and good antimicrobial
activity 0.90 mg/mL in comparison with the reference compound kanamycin (0.50 mg/mL).
Noteworthy, the antifungal activity of bromide 9 is higher than that reported for cinnamosmolide
(
2) (Canonica et al. 1969).
3
3
. Experimental
.1. General experimental procedure
Melting points (m.p.) were taken on a Boethius (VEB Analytik, DDR) hot stage apparatus.
Optical rotations were determined on a Perkin-Elmer 241 polarimeter (Perkin-Elmer,
Norwalk, CT, USA) with a 1 dm microcell, in CHCl . IR spectra were obtained on Bio-Rad-
3
Win-IR (Bio-Rad, Cambridge, MA, USA) and Perkin-Elmer spectrometers (Perkin-Elmer,
1
Norwalk, CT, USA). H and C NMR spectra were recorded in CDCl on Bruker AC-E 200
13
3
(
(
Bruker BioSpin, Rheinstetten, Germany) and Bruker Avance DRX 400 spectrometers
Bruker BioSpin, Rheinstetten, Germany). Chemical shifts are given in ppm in d scale and
referred to CHCl (dH at 7.26 ppm) and to CDCl (d 77.00 ppm), respectively. Coupling
3
3
C
constants (J) are reported in Hertz (Hz). The H, H-COSY, H, C-HSQC and H, C-HMBC
experiments were recorded using standard pulse sequences, in the version with z-gradients, as
delivered by Bruker Corporation (Bruker BioSpin, Rheinstetten, Germany). Carbon
substitution degrees were established by the DEPT pulse sequence. For analytical TLC,
Sorbfil silica-gel plates were used. The TLC plates were sprayed with conc. H SO and heated
2
4
at 808C for 5 min. Column chromatography was carried out on Across silica gel (60–200
mesh) using petroleum ether (PE) (b.p. 40–608C) and the gradient mixture of PE and

4
A. Ciocarlan et al.
EtOAc. All solvents were purified and dried by standard techniques before use. Solutions in
organic solvents were dried over anhydrous Na SO , filtered and evaporated under reduced
pressure.
2
4
3.1.1. (1S,2R)-2-Hydroxy-1,3,7,7-tetramethyl-5-oxobicyclo[4.4.0]dec-3-en-2-ylmethyl
acetate (8)
To a solution of 7 (100 mg, 0.40 mmol), prepared by the procedure of Vlad et al. (2013), in dry
Py (5 mL), Ac O (0.5 mL) was added and the resulted mixture was stirred overnight at room
2
temperature. Then the reaction mixture was diluted with water (30 mL) and extracted with
diethyl ether (3 £ 20 mL). After solvent removal the crude product (119 mg) was subjected to
column chromatography on SiO (12 g, eluent: PE–EtOAc 4:1) to afford 8 (112 mg, 96%) as
2
2
0
white solid (MeOH), m.p. 87–888C, ½aꢀ 2 9.5 (c ¼ 1.0, CHCl ); IR (CHCl ) n 3620, 3505,
D
21 1
3
3
2
1
923, 2950, 1755, 1674, 1230, 901 cm . H NMR (CDCl , 400 MHz, ppm): d 5.76 (1H, d,
3
.2 Hz, H-7), 4.38 (1H, d, 12.4 Hz) and 4.26 (1H, d, 12.4 Hz, H-11), 2.81 (1H, s, H-5), 2.14 (3H,
s, OAc), 1.94 (3H, d, 1.6 Hz, H-12), 1.20 (3H, H-15), 1.20 2 1.90 (7H, m), 1.16 (3H, s, H-13),
1
.03 (3H, s, H-14); C NMR (CDCl , 100 MHz, ppm): d 199.7 (C-6), 170.9 (CvO), 152.9 (C-
), 129.9 (C-7), 75.1 (C-9), 64.7 (C-11), 55.3 (C-5), 45.6 (C-10), 42.4 (C-3), 33.8 (C-14), 32.2
3
1
8
3
(C-4), 31.9 (C-1), 21.8 (C-13), 21.1 (OAc), 19.80 (C-12), 18.1 (C-2), 17.9 (C-15); C H O
17 26 4
found (%) C, 69.58; H, 9.05; required (%) C, 69.36; H, 8.90.
3
.1.2. (1S,2S)-3-Bromomethyl-2-hydroxy-1,7,7-trimethyl-5-oxobicyclo[4.4.0]dec-3-en-
-ylmethyl acetate (9)
2
To a solution of 8 (200 mg, 0.68 mmol) in dry CCl (10 mL), NBS (363 mg, 2.04 mmol) was
4
added and the resulted mixture was refluxed for 9 h. After cooling, the reaction mixture was
filtered and the solvent removed to yield the crude product (260 mg), which was purified by
column chromatography on SiO (23 g, eluent: PE–EtOAc 4:1) to afford 9 (230 mg, 91%) as
2
2
D
0
white solid (MeOH), m.p. 80–818C; ½aꢀ –16.7 (c ¼ 0.6, CHCl ); IR (CHCl ) n 3578, 2954,
3
3
21 1
930, 1730, 1675, 1350, 1210, 1015, 945, 780 cm . H NMR (CDCl , 400 MHz, ppm): d 6.03
3
2
(
1H, s, H-7), 4.54 (1H, d, 12.4 Hz) and 4.38 (1H, d, 12.4 Hz, H-11), 4.19 (1H, d, 11.2 Hz) and
.13 (1H, d, 11.2 Hz, H-12), 2.96 (1H, s, H-5), 2.18 (3H, s, OAc), 2.04–1.17 (7H, m), 1.18 (3H,
4
s, H-15), 1.16 (3H, s, H-13), 1.02 (3H, s, H-14); C NMR (CDCl , 100 MHz, ppm): d 199.7 (C-
1
3
3
6
), 170.7 (CvO), 149.9 (C-8), 132.9 (C-7), 75.3 (C-9), 64.1 (C-11), 55.6 (C-5), 46.2 (C-10),
2.2 (C-3), 33.5 (C-14), 32.2 (C-4), 31.8 (C-1), 31.4 (C-12), 21.7 (C-13), 21.1 (OAc), 18.0 (C-2),
7.8 (C-15); C H O Br found (%) C, 54.51; H, 6.60; Br, 21.13; required (%) C, 54.70; H, 6.75;
4
1
1
7 25 4
Br, 21.41.
3.1.3. (1S,2S)-2-Hydroxy-1,7,7-trimethyl-2-methylcarbonyloxymethyl-5-oxobicyclo-[4.4.0]
dec-3-en-3-ylmethyl acetate (10)
The mixture of 9 (165 mg, 0.42 mmol) and KOAc (82 mg, 0.84 mmol) in dry dimethyl
sulphoxide (DMSO) (5 mL) was stirred for 1 h at room temperature, then diluted with H O
2
(
10 mL) and extracted with Et O (3 £ 15 mL). Next the organic layer was washed with H O (3
2
2
£
10 mL) and dried. After solvent removal the crude product was purified by column
2
D
1 1
1
chromatography on SiO (15 g, PE–EtOAc 4:1) to afford 10 (153 mg, 98%), as oil, ½aꢀ þ23.1
2
2
(
(
c ¼ 0.8, CHCl ); IR (film): n 3595, 3475, 2943, 1725, 1664, 1342, 1197, 1098 cm . H NMR
3
CDCl , 400 MHz, ppm): d 5.98 (1H, s, H-7), 4.81 (1H, d, 15.2 Hz) and 4.67 (1H, d, 15.2 Hz, H-
3
1
2
1), 4.39 (1H, d, 12.4 Hz) and 4.29 (1H, d, 12.0 Hz, H-12), 2.88 (1H, s, H-5), 2.13 (3H, s, OAc),
1
.12 (3H, s, OAc), 1.20 (3H, s, H-15), 1.15 (3H, s, H-13), 1.03 (3H, s, H-14). C NMR (CDCl3,
3

Natural Product Research
5
1
00 MHz, ppm): d 199.6 (C-6), 170.9 (CvO), 170.6 (CvO), 150.1 (C-8), 128.9 (C-7), 74.6 (C-
), 64.4 (C-11), 62.7 (C-12), 55.6 (C-5), 45.8 (C-10), 42.3 (C-3), 33.6 (C-14), 32.2 (C-4), 31.4
9
(
C-1), 21.8 (C-13), 21.0 (OAc), 20.9 (OAc), 17.9 (C-15), 17.8 (C-2); C H O found (%) C,
19 28 6
6
4.51; H, 7.73; required (%) C, 64.75; H, 8.00.
3.1.4. (5S,6S)-5-Hydroxy-4,5-di(hydroxymethyl)-6,10,10-trimethylbicyclo[4.4.0]dec-3-en-2-
one (11)
To a solution of 10 (130 mg, 0.37 mmol) in MeOH (1.5 mL), a saturated solution of K CO in
2
3
MeOH (7 mL) was added. The reaction mixture was stirred for 0.5 h at room temperature, diluted
with H O (15 mL) and extracted with Et O (3 £ 10 mL), then the organic layer was washed with
2
2
H O (3 £ 10 mL) and dried. After solvent removal, the crude product (103 mg) was subjected to
2
column chromatography on SiO (10 g, PE–EtOAc 7:3) to give 11 (98 mg, 99%) as white solid
2
2
D
1
(
MeOH), m.p. 121–1228C; literature not reported (Urones et al. 1997; Zhou et al. 2011); ½aꢀ
21 1
2
D
0
2
26.6 (c ¼ 0.4, MeOH), literature ½aꢀ 2 62.48 (c ¼ 0.94, MeOH) (Urones et al. 1997); IR
(
d 5.87 (1H, s, H-7), 4.49 (1H, d, 14.0 Hz) and 4.30 (1H, d, 14.0 Hz, H-12), 3.86 (2H, s, H-11),
CHCl ): n 3625, 3448, 2960, 1670, 1460, 1215, 1080 cm . H NMR (CDCl , 400 MHz, ppm):
3 3
1
3
2
1
5
1
.87 (1H, s, H-5), 1.19 (3H, s, H-15), 1.15 (3H, s, H-13), 0.94 (3H, s, H-14). C NMR (CDCl3,
00 MHz, ppm): d 200.7 (C-6), 153.4 (C-8), 128.8 (C-7), 75.1 (C-9), 64.8 (C-11), 62.2 (C-12),
6.1 (C-5), 45.3 (C-10), 42.3 (C-3), 33.6 (C-14), 32.2 (C-4), 31.2 (C-1), 21.8 (C-13), 17.9 (C-15),
7.7 (C-2); C H O found (%) C, 67.31; H, 9.23; required (%) C, 67.14; H 9.01.
1
5 24 4
3.1.5. (9aS,9bS)-9b-hydroxy-6,6,9a-trimethyl-1,3,5,5a,6,7,8,9,9a,9b-decahydrobenzo[e]-
isobenzofuran-3,5-dione (12)
To a solution of 11 (30 mg, 0.112 mmol) in CH Cl (3 mL), MnO (195 mg, 2.24 mmol) was
2
2
2
added. The reaction mixture was stirred for 70 h at room temperature, then filtered through SiO2
CH Cl ). After solvent removal lactone 12 (26 mg, 93%) was obtained, as white solid (PE), m.
(
2
2
2
D
1
p. 195–1968C, literature not reported (Kubo et al. 1983; Burke et al. 1991); ½aꢀ 2 35.16
(
c ¼ 0.3, CHCl ), literature not reported (Kubo et al. 1983; Burke et al. 1991); IR (CHCl ): n
3
3
2
434, 2974, 1770, 1625, 1490, 1190, 1140, 1115 cm . H NMR (CDCl , 400 MHz, ppm): d
1 1
3
6
1
1
4
1
3
.50 (1H, s, H-7), 4.53 (1H, d, 10.2 Hz) and 4.37 (1H, d, 10.2 Hz, H-11), 2.96 (1H, s, H-5), 2.40-
1
3
.35 (2H, m), 1.18 (3H, s, H-15) 1.17 (3H, s, H-14), 1.08 (3H, s, H-13); C NMR (CDCl3,
00 MHz, ppm): d 199.3 (C-6), 168.4 (C-12), 141.8 (C-8), 131.0 (C-7), 74.9 (C-9), 55.7 (C-5),
5.5 (C-10), 42.6 (C-3), 33.5 (C-14), 32.3 (C-4), 31.5 (C-1), 30.9 (C-11), 21.3 (C-13), 19.6 (C-
5), 17.2 (C-2); (C H O found (%) C, 67.96; H 7.48; required (%) C, 68.16; H 7.63).
1
5 20 4
3
.2. Antimicrobial and antifungal activity
Fungi: A. niger ATCC 53346, P. frequentans ATCC 10110 and A. alternata ATCC 8741, and
Gram-negative bacteria P. aeruginosa ATCC 27813 and Gram-positive B. polymyxa were
provided by the American Type Culture Collection (ATCC, USA).
Compounds caspafugin and kanamycin, both from Liofilchem (Roseto degli Abruzzi, Italy),
were used as standards for antifungal and antibacterial activity testing. After 48 h of incubation,
a symmetrical inhibition ellipse centred along the strip was formed. The MIC is read directly
from the scale in terms mg/mL, at the point where the edge of the inhibition ellipse intersects
with the MIC test strip.
Sample solutions of 0.5%, 1% and 2% concentrations were obtained by dissolution of
appropriate amounts of tested compounds 7–12 in fixed volumes of DMSO.

6
A. Ciocarlan et al.
It must be mentioned that for fungi, Sabouraud agar medium with dextrose was used (4%,
SDA), and for bacteria a Standard I nutrient agar medium was used, both from Merck
(
Schwalbach Hesse, Germany).
Microorganism suspensions were prepared using the method of successive agar dilutions
according to the standard MIC (Usta et al. 2007) and their cultivation was carried out according
to standard procedures (SR-EN 1275:2006 and NCCLS guidelines) (NCCLS 2003). The final
2
4
charge-stock inoculum was prepared as 1 £ 10 mg/mL concentration and inoculated plates
were incubated at 318C for 7 days. First observations were made after 48 h and final observations
after 7 days of incubation, establishing the MIC. Observations on the results were made by visual
analysis, microscopy and photography, using a stereomicroscope Novex Ap-8 Euromex
(
(
Olimpus Europa Holding G.m.b.H., Hamburg, Germany) and Olympus SZY 160 microscope
Olympus Corporation, Shinjuku, Tokyo, Japan).
4
. Conclusions
Thus, starting from (þ)-larixol (3) via intermediate 6-oxo-7-drimen-9a,11-diol (7), the formal
synthesis of (2)-pereniporin B (1) and (2)-cinnamosmolide (2) has been achieved in nine steps
leading to lactone 12 in ,20% overall yield.
Acknowledgements
The support from the Project No. 264115 (STREAM) in the frame of EU funded FP7-REGPOT-2010-1 call
is acknowledged by the authors from the ‘Petru Poni Institute’.
References
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