Total synthesis of Z-isomer of phomolide B

Article abstract of DOI:10.1016/j.tetlet.2010.11.003

We have achieved the synthesis of Z-isomer of phomolide B during our investigation toward the effect of protecting group on the outcome of ring-closing metathesis reaction. The other key reactions involved are cis-selective partial hydrogenation, Sharples

Full text of DOI:10.1016/j.tetlet.2010.11.003

Tetrahedron Letters 52 (2011) 151–154
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Total synthesis of Z-isomer of phomolide B
⇑
⇑
Debendra K. Mohapatra , D. Prabhakar Reddy, Uttam Dash, J. S. Yadav
Organic Chemistry Division-I, Indian Institute of Chemical Technology (CSIR), Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
We have achieved the synthesis of Z-isomer of phomolide B during our investigation toward the effect of
protecting group on the outcome of ring-closing metathesis reaction. The other key reactions involved are
cis-selective partial hydrogenation, Sharpless asymmetric epoxidation, Yamaguchi esterification, and fol-
lowing 12 longest linear sequence with 18.5% overall yield starting from a known intermediate 20.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 6 October 2010
Revised 29 October 2010
Accepted 2 November 2010
Available online 5 November 2010
Keywords:
Phomolide B
Decanolides
Sharpless asymmetric epoxidation
Yamaguchi esterification
Ring-closing metathesis
Natural resources such as plants, animals, and microorganisms
constitute a rich and versatile source of bioactive chemicals; many
of them and their synthetic derivatives have been proven to be ben-
eficial to human health. Many naturally occurring 10-membered
lactones isolated from fungal metabolites, commonly known as
decanolides, have attracted considerable attention from synthetic
R5
Me
O
Me
OH
O
OH
O
OH
H
O
O
O
O
R3
O
OH
H
O
Me
O
O
R2
OH
Me
R1
4. Stagonolide D
5. Stagonolide E
6. Stagonolide F
1-3
7. Stagonolide G
1. Stagonolide A. R1 = H, R2+R3 = O, R4 = OH, R5 = propyl
2. Stagonolide B. R1 = b-OH, R2 = H, R3 = OH, R4 = OH, R5 = propyl
1
2
3
4
5
3. Stagonolide C.
R = a-OH, R = OH, R = H, R = H, R = Me
OH
HO
OH
Me
O
H
OH
OH
OH
O
O
O
O
O
O
H
OH
O
O
Me
O
Me
O
Me
OH
8. Stagonolide H
9. Stagonolide I
10. Modiolide A
11. Herbarumin III
12. Nonenolide
Me
O
Me
OH
O
O
O
HO
O
O
O
O
OH
OH
O
15. Phomolide A
O
OH
13. Decarestrictine C1
14. Decarestrictine C2
16. Phomolide B
Figure 1. Stagonolides A-I, modiolide A, herbarumin III, nonenolide, decarestrictine C1 and C2 and phomolide A and B.
⇑
Corresponding authors. Tel.: +91 40 27193128; fax: +91 40 27160387 (D.K.M.).
E-mail address: mohapatra@iict.res.in (D.K. Mohapatra).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.11.003

152
D. K. Mohapatra et al. / Tetrahedron Letters 52 (2011) 151–154
organic chemists as well as bioorganic chemists, because of their
interesting structural features and exhibit various biological activ-
ities like plant growth inhibition, anti-feedant, anti-fungal and
anti-bacterial activities.1 The phytotoxic metabolites such as stag-
onolides A-I (1–9),2 modiolide A (10),3 herbarumin III (11),4 non-
enolide (12),5 and decarestrictine C1 (13) and C2 (14)6 have
already been isolated and well characterized in recent years
(Fig. 1). Two other structurally similar 10-membered lactones
phomolide A (15) and phomolide B (16)7 have been isolated from
the culture of Phomopsis sp. hzla01-1. These compounds have the
double bond geometry by the protecting groups during the ring-
closing metathesis reaction.
Asa partof our ongoing programinexploringring-closing metath-
esis for macrolides synthesis, we investigated the use of ring-closing
metathesis reaction in the total synthesis of phomolide B.
According to our retrosynthetic analysis, the target phomolide
could be achieved by ring-closing metathesis (RCM) of the diolefi-
nic ester 17 which in turn could be prepared via esterification of
the alcohol 18 and acid 19.
These two fragments could be prepared from known chiral
epoxide 20 and commercially available 1,3-propane diol 21,
respectively (Scheme 1).
The synthesis of alcohol fragment 18 began with the regeoselec-
tive epoxide ring opening of known epoxide 2010 with ethylmag-
nesium bromide to afford the chiral alcohol 22 in 92% yield.
Protection of the hydroxy group present in 22 with TBDPSCl, imid-
azole in CH2Cl2 furnished 23 in 95% yield. Selective deprotection of
p-methoxybenzyl group with DDQ11 in CH2Cl2/water (9:1) system
yielded the primary hydroxy compound 24 in 90% yield. The pri-
mary hydroxy group present in 24 was oxidized with IBX12 in
significant antimicrobial activities against
CMCC44103, Candida albicans AS2.538, Saccharomyces cerevisiae
ATCC9763 with MICs 5–10 g/mL.
Escherichia coli
l
Construction of lactones through the formation of C–C bond and
particularly by intramolecular ring-closing metathesis8 reaction
stands as a promising tool for decanolides. The influence of the
protecting groups in the geometrical outcome of the ring-closing
metathesis reaction has been reported previously.9 During our
studies on the total synthesis of nonenolide9e (12) and decarestric-
tine9c C1 (13) and C2 (14), we observed a complete control of the
O
1) TPP, Imid., I 2
O
TBDPSO
O
HO
PMBO
THF, 0 oC, 15 min
ref. 19
HO
OH
OH
O
2) Zn dust, NaI
MeOH, reflux, 4 h
81% for two steps
O
30
21
O
O
17
16
OH
OPMB
NaH, PMBBr, THF
0 oC-rt, 4 h, 89%
O
OPMB
OH
TBDPSO
TBDPSO
O
+
HO
HO
31
32
19
18
1) TEMPO, BAIB, 0 oC
O
OPMB
OH OPMB
CSA, MeOH
O
oC-rt, 94%
2) NaClO2, NaH2PO4
tBuOH-H2O, 0 oC-rt
82% over two steps
HO
0
OH
OPMB
33
19
21
20
Scheme 1. Retrosynthetic analysis of phomolide B.
Scheme 3. Synthesis of fragment 19.
OH
OTBDPS
O
EtMgBr, CuCN
TBDPSCl, Imid.
OPMB
CH2Cl2, 0 oC-rt
1 h, 95%
THF, 0 oC
10 min, 92%
OPMB
OPMB
20
22
23
1) IBX, DMSO -THF
0 oC-rt, 2 h
OTBDPS
OTBDPS
DDQ, CH2Cl2/H2O
n-BuLi, (HCHO)n
OH
0 oC-rt, 2 h, 90%
2) Bestmann reagent
K2CO3, MeOH,
0 oC-rt, 4 h
THF, -78 oC-rt
6 h, 82%
25
24
72% for two steps
OTBDPS
Lindlar Catalyst
OTBDPS
L-(+)-DET, Ti (OiPr)4, TBHP
CH2Cl2, - 20 oC, 24 h, 84%
OH
Pd-CaCO3, H2
27
EtOAc, quinoline
rt, 12 h, 98%
26
OH
1) DMP, CH 2Cl2
OTBDPS
OH
0 oC-rt, 1 h
OTBDPS
TBAF, THF
O
O
O
0 oC-rt, 2 h, 94%
2) PPh3CH3Br
NaHMDS, THF
0 oC-rt, 2 h
18
29
28
OH
78% for two steps
Scheme 2. Synthesis of fragment 18.

D. K. Mohapatra et al. / Tetrahedron Letters 52 (2011) 151–154
153
O
2,4,6-Trichlorobenzoyl
PMBO
OH
chloride, Et3N, DMAP
O
OPMB
O
+
O
THF, Toluene, 0 oC-rt
4 h, 92%
HO
O
18
19
17
Grubbs-II
CH2Cl2, reflux
8 h, 78%
O
DDQ, CH2Cl2/H2O
0 oC-rt, 2 h, 90%
PMBO
O
O
O
HO
34
O
DDQ, CH2Cl2/H2O
0
oC-rt, 2 h, 92%
O
35
O
HO
Grubbs-II
O
CH2Cl2, reflux
8 h, 76%
O
36
Scheme 4. Total synthesis of Z-isomer of phomolide B.
DMSO and THF to afford the corresponding aldehyde which in turn
without further purification treated with Bestmann’s reagent13 in
presence of K2CO3 in MeOH to furnish the corresponding alkyne
25 in 72% yield over two steps. Treatment of the compound 25
with paraformaldehyde in presence of n-BuLi at ꢀ78 °C in THF
afforded the propargyl alcohol derivative 26 in 82% yield.14 The al-
kyne 26 was then subjected to react with Lindlar’s catalyst15 under
H2 atmosphere in ethyl acetate to produce the required Z-config-
ured allyl alcohol 27 in 98% yield. Sharpless asymmetric epoxida-
tion16 of 27 with (+)-DET/Ti(OiPr)4/TBHP in CH2Cl2 gave the
epoxide 28 with required stereoisomer in 84% yield (Scheme 2).
Subsequent oxidation of the epoxy alcohol 28 with Dess-Martine
periodinane17 in CH2Cl2 followed by one carbon homologation
with Ph3P=CH2 gave the corresponding vinyl epoxide 29 in 78%
yield over two steps. Deprotection of the sillyl ether with TBAF18
in THF afforded the required fragment 18 in 94% yield.
was established as ‘‘Z’’ from its coupling constants, while one of
the olefinic proton signal appeared at d 5.70 ppm as a ddd
(J = 1.5, 6.9, 11.5 Hz) and the signal due to other double proton ap-
peared at d 5.57 ppm as a dd (J = 5.2, 11.5 Hz). Finally, deprotection
of the PMB group present in 34 with DDQ in CH2Cl2/water (9:1)
system furnished the Z-isomer of phomolide B 3626 in 92% yield.
Now, our next task was to deprotect the PMB group present in
17 and verify the outcome of the geometry of the double bond
using the same conditions as followed for the ring-closing metath-
esis reaction in Scheme 3. Deprotection of the PMB group present
in 17 with DDQ in CH2Cl2/water (9:1) system furnished 35 in 90%
yield. Finally, reaction of diene 3527 (0.0011 M in CH2Cl2) in pres-
ence of 10 mol% Grubbs’ second-generation catalyst in this case
also afforded exclusively Z-isomer of phomolide B 36 in 76% yield.
Similar results are already reported in the literature28 which nicely
exemplifies the substrate specific nature of the reaction.
The synthesis of the acid fragment 19 started from a known
intermediate 30,19 which was prepared from commercially avail-
able 1,3-propane diol 21. The epoxy alcohol 30 was converted into
its iodo derivative with triphenylphosphine, iodine, and imidazole
in THF, followed by zinc mediated reductive elimination furnished
the allyl alcohol 31.20 The allyl alcohol 31 was then protected as its
PMB ether with PMBBr and NaH in THF and subsequent deprotec-
tion of the sillyl group with CSA in MeOH gave the corresponding
alcohol 33 in 83% yield over two steps. Acid 19 was obtained by
a two step sequence in 82% yield; in the first step oxidation of
the compound 33 with TEMPO, BAIB21 in CH2Cl2 furnished the cor-
responding aldehyde and in the second step, further oxidation un-
der Pinnick conditions22 (NaClO2/NaH2PO4/t-BuOH/H2O/2-methyl-
2-butene) afforded acid 19 (Scheme 3).
In summary, effect of protecting group in the outcome of the
double bond geometry during ring-closing metathesis reaction
was studied in case of total synthesis of phomolide B which led
to exclusive formation of its Z-isomer. Introduction of the
E-geometry for the synthesis of phomolide B following intramolec-
ular asymmetric Nozaki-Hiyama-Kishi reaction is under progress
in our laboratory and will be reported in due course.
Acknowledgments
DPR and UD thank Council of Scientific and Industrial Research
(CSIR), New Delhi, India, for the financial assistance in the form of
research fellowships.
With alcohol 18 and acid fragment 19 in hand, our next target
was to couple both the fragments and verify the geometrical out-
come of the ring-closing metathesis with and without the protect-
ing group. Accordingly, the two fragments, acid 19 and alcohol 18
were esterified under Yamaguchi conditions23 (2,4,6-trichloroben-
zoyl chloride/Et3N/THF then DMAP/toluene) to furnish the diene
1724 in 92% yield. Treatment of the ester 17 (0.001 M dilution in
degassed CH2Cl2) with Grubbs’ II generation catalyst under re-
fluxed conditions afforded the lactone 3425 with Z-configured ole-
fin as a sole product (Scheme 4). Integrity of compound 34 was
ascertained by its spectral data. The geometry of the olefin in 34
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.11.003.
References and notes
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24. Spectral and analytical data of 17: ½a D27
ꢁ
-9 (c 1.1, MeOH); IR (neat) mmax 3089,
2925, 1763, 1617, 1513, 1461, 1376, 1243, 1178, 1056 cmꢀ1
;
1H NMR
(300 MHz, CDCl3): d 7.14 (d, J = 8.5 Hz, 2H), 6.78 (d, J = 8.5 Hz, 2H), 5.84–5.56
(m, 2H), 5.47–5.19 (m, 4H), 5.04 (m, 1H), 4.47 (d, J = 11.1 Hz, 1H), 4.25 (d,
J = 11.1 Hz, 1H), 4.22 (m, 1H), 3.78 (s, 3H), 3.28 (dd, J = 4.3, 6.7 Hz, 1H), 3.04 (m,
1H), 2.56 (m, 1H), 2.41 (m, 1H), 1.72 (m, 1H), 1.54 (m, 1H), 1.43–1.23 (m, 4H),
0.89 (t, J = 7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3): d 170.53, 159.42, 137.34,
132.33, 130.26, 129.39, 120.64, 118.04, 113.71, 77.03, 71.99, 70.31, 56.92,
55.62, 55.27, 41.30, 36.47, 32.72, 18.61, 13.84; MS (ESI): m/z = 375 [M+1]+, 398
[M+Na]+.
7. Du, X.; Lu, C.; Li, Y.; Zheng, Z.; Shen, Y. J. Antibiot. 2008, 61, 250.
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25. Spectral and analytical data of 34: ½a D27
ꢁ
+46 (c 1.8, MeOH); IR (neat) mmax 3089,
2960, 1724, 1617, 1513, 1461, 1376, 1243, 1178, 1056 cmꢀ1
;
1H NMR
(300 MHz, CDCl3): d 7.27 (d, J = 8.5 Hz, 2H), 6.89 (d, J = 8.5 Hz, 2H), 5.7 (ddd,
J = 1.5, 6.9, 11.5 Hz, 1H), 5.57 (dd, J = 5.2, 11.5 Hz, 1H), 5.13 (m, 1H), 4.62–4.38
(m, 3H), 3.81 (s, 3H), 3.40 (m, 1H), 2.97 (dt, J = 3.5, 10.9 Hz, 1H), 2.70 (dd, J = 3.3,
6.9 Hz, 1H), 2.42 (t, J = 11.3 Hz, 1H), 2.20 (m, 1H), 1.64 (m, 1H), 1.43–1.22 (m,
4H), 0.91 (t, J = 7.17 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d 170.59,
159.38, 135.24, 130.30, 129.62, 129.54, 113.93, 73.04, 71.28, 70.51, 57.15,
55.25, 53.39, 41.23, 36.48, 36.35, 18.64, 13.68; MS (ESI): m/z = 347 (M+1)+, 369
[M+Na]+.
26. Spectral and analytical data of 36: ½a D27
+68 (c 0.5, MeOH); IR (neat) mmax 3445,
ꢁ
2959, 2924, 2870, 1723, 1649, 1543, 1432, 1389, 1280, 1126, 1069, 1025 cmꢀ1
;
1H NMR (300 MHz, CD3OD): d 5.66 (ddd, J = 1.8, 8.1, 11.5 Hz, 1H), 5.36 (dd,
J = 5.4, 11.5 Hz, 1H), 5.12 (m, 1H), 4.75 (m, 1H), 3.47 (m, 1H), 2.92 (dt, J = 3.9,
10.9 Hz, 1H), 2.56 (dd, J = 3.5, 10.3 Hz, 1H), 2.35 (t, J = 11.3 Hz, 1H), 2.17 (dd,
J = 1.8, 10.9 Hz, 1H), 1.57 (m, 1H), 1.39–1.18 (m, 4H), 0.90 (t, J = 7.3 Hz, 3H); 13
C
NMR (75 MHz, CD3OD): d 172.23, 137.66, 128.23, 72.65, 68.24, 58.50, 54.56,
44.59, 37.62, 37.46, 19.74, 14.03; MS (ESI): m/z = 249 [M+Na]+.
27. Spectral and analytical data of 35: ½a D27
ꢁ
ꢀ6 (c 0.8, MeOH); IR (neat) mmax 3442,
1H NMR
3089, 2959, 2927, 2871, 1639, 1485, 1412, 1128, 1021 cmꢀ1
;
(300 MHz, CDCl3): d 5.94–5.75 (m, 2H), 5.53–5.23 (m, 4H), 5.18–5.07 (m,
2H), 4.50 (m, 1H), 3.35 (dd, J = 4.3, 6.4 Hz, 1H), 3.12 (dd, J = 3.2, 8.3 Hz, 1H),
2.58–2.42 (m, 2H), 1.73–1.22 (m, 6H), 0.94 (t, J = 7.1 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d 171.61, 138.78, 132.14, 120.84, 115.183, 72.31, 68.75,
57.85, 55.38, 36.38, 32.71, 32.41, 18.55, 13.78; MS (ESI): m/z = 255 [M+1]+, 277
[M+Na]+.
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