Stereoselective first total synthesis, confirmation of the absolute configuration and bioevaluation of botryolide-E

Article abstract of DOI:10.1016/j.bmcl.2010.12.024

A simple, first stereoselective total synthesis of botryolide-E has been described. The synthesis started from propylene oxide employing Jacobsen's hydrolytic kinetic resolution (HKR), selective epoxide opening, sharpless asymmetric dihydroxylation, one p

Full text of DOI:10.1016/j.bmcl.2010.12.024

Bioorganic & Medicinal Chemistry Letters 21 (2011) 997–1000
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Stereoselective first total synthesis, confirmation of the absolute
configuration and bioevaluation of botryolide-E
D. Kumar Reddy a, V. Shekhar a, P. Prabhakar a, D. Chanti Babu a, D. Ramesh a, B. Siddhardha b,
U. S. N. Murthy b, Y. Venkateswarlu a,
⇑
a Natural Products Laboratory, Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500 007, India
b Division of Biology, Indian Institute of Chemical Technology, 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:
A simple, first stereoselective total synthesis of botryolide-E has been described. The synthesis started from
propylene oxide employing Jacobsen’s hydrolytic kinetic resolution (HKR), selective epoxide opening,
sharpless asymmetric dihydroxylation, one pot acetonide deprotection and lactonization as key steps. Fur-
ther, the synthesis confirms the absolute configuration of the natural product botryolide-E and we evalu-
ated the biological behavior of natural product botryolide-E against a panel of bacteria and fungi.
Received 3 October 2010
Revised 16 November 2010
Accepted 7 December 2010
Available online 10 December 2010
Botryolide-E exhibits significant potent activity against Staphylococcus aureus (MTCC 96) (6.25
against Escherichia coli (MTCC 443) (12.5 g/ml), Bacillus subtilis (MTCC 441) (25 g/ml) and compound 1
exhibited good to moderate antifungal activity.
lg/ml), good
Keywords:
l
l
c
-Lactone
Botryolide-E
Jacobsen’s hydrolytic kinetic resolution
(HKR)
Ó 2010 Elsevier Ltd. All rights reserved.
Sharpless asymmetric dihydroxylation
Staphylococcus aureus
Antimicrobial
The emergence of multidrug resistance among pathogens repre-
sents a significant challenge for medical professionals.1 Particular
concern are methicillin-resistant Staphylococcus aureus (MRSA)2
and vancomycin-resistant enterococci (VRE), due to the combina-
tion of increasing prevalence and recalcitrance to therapy.3 One
important strategy to address these resistance issues is the develop-
ment of new classes of antibiotic drugs with significant activity
against resistant pathogens. In addition, increase in immuno com-
promised patients and hospital acquired infections has necessitated
the exploration of new biological targets and discovery of effective
antibacterial and antifungal agents. The natural products containing
did not show any activity. In continuation of our interest towards the
total synthesis of biologically active lactone containing natural
products,9 we planned to synthesize compound 1 and evaluate the
antibacterial activity against Bacillus subtilis (MTCC 441), S. aureus
(MTCC 96), Staphylococcus epidermidis (MTCC 437), Pseudomonas
aeruginosa (MTCC 741), Klebsiella pneumonia (MTCC 39) and Esche-
richia coli (MTCC 443) and antifungal activity against Rhizopus oryzae
(MTCC 262), Aspergillus niger (MTCC 1344), Candida albican (MTCC
227), and Saccharomyces cerevisiae (MTCC 171). To the best our
knowledge, the synthesis of 1 has not been reported in the literature
and herein we report on simple efficient stereoselective synthesis
from commercially available propylene oxide employing Jacobsen’s
hydrolytic kinetic resolution (HKR), epoxide opening, Sharpless
asymmetric dihydroxylation, one pot acetonide deprotection and
lactonization as the key steps.
c
-lactonemotifareknowntoshow varietyofactivities4 suchascyto-
toxic,5 antitumor,6 cyclooxygenase or phospholipase A2 inhibition.7
Theseareofeitherbacterialorfungalorigin. Botryolide-E(1), a -lac-
c
tone has been isolated from cultures of the fungicolous Botryotri-
chum sp. (NRRL 38180) by Gloer and co-workers in 2008.8 The
structure and relative configuration was established through a
NMR and ESIMS data, respectively. Due to a limitation of isolated
compound 1 (1 mg), the authors were unable to evaluate its antibac-
terial activity.8 Other isolated compounds such as botryolides A, B, D
O
O
O
O
HO
1
Retrosynthetically (Scheme 1), we envisaged that our target
molecule botryolide-E (1) can be obtained from olefinic intermedi-
ate 14 by one pot acetonide deprotection and lactonization.
⇑
Corresponding author. Tel.: +91 40 27193167; fax: +91 40 27160512.
E-mail address: luchem@iict.res.in (Y. Venkateswarlu).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.12.024

998
D. K. Reddy et al. / Bioorg. Med. Chem. Lett. 21 (2011) 997–1000
O
O
O
O
HO
O
O
O
O
O
O
O
14
1
2
Scheme 1. Retrosynthetic route for botryolide-E.
As outlined in Scheme 1, the propylene oxide 2 was subjected to
Jacobsen’s HKR using (R,R)-salen-Co-(OAc) catalyst (Fig. 1) to afford
R-propylene oxide 3 as a single isomer ½a D25
ꢀ
+11.7 (c 1, CHCl3), [lit.
H
H
for S-propylene oxide ½a D25
ꢀ
ꢁ11.6 (neat)]10 (Scheme 2). The R-pro-
N
Co
O
N
pylene oxide 3 was easily isolated from the more polar diol 3a by
distillation (Scheme 2).
t-Bu
t-Bu
O
The enantiomeric pure propylene oxide 3 was subjected to regio-
selective ring opening with THP protected propargyl alcohol using
n-BuLi, BF3OEt to furnish alcohol 4.11 The secondary hydroxyl group
in 4 was protected with tert-butyldiphenylsilyl chloride and imidaz-
ole in the presence of a catalytic amount of DMAP to afford the silyl
ether 5, which on depyranylnation using PPTS in methanol afforded
compound 6. The free progargylic alcohol 6 was reduced with Red-Al
(3 equiv) to afford allylic alcohol 7. The tert-butyldiphenylsilyl ether
in compound 7 was deprotected to form diol 8 in which the primary
alcohol was selectively protected using tert-butyldimethylsilily
chloride to afford monosilyl ether 9. The secondary hydroxyl group
in monosilyl ether 9 was acetylated using acetic anhydride in
pyridine to afford acetylated compound 10. Compound 10 on diaste-
reo and enantioselective Sharpless asymmetric dihydroxylation
OAc
t-Bu
t-Bu
Fig. 1. (R,R)-salen-Co(III)-(OAc) complex.
OH
O
OH
O
a
+
2
3
3a
Scheme 2. Reagents and conditions: (a) (R,R)-salen-Co-(OAc) (0.5 mol%), distd H2O
(0.55 equiv), 0 °C, 14 h, (43% for 3, 40% for 3a).
afforded single diastereomer 11 {½a D25
ꢀ
: ꢁ39.5 (c 0.25, CHCl3)}.12
Intermediate 14 in turn prepared from propylene oxide 2 via
Jacobsen’s hydrolytic kinetic resolution (HKR), selective epoxide
opening, sharpless asymmetric dihydroxylation as key steps.
The diol 11 was protected with 2,2-dimethoxypropane in the
presence of a catalytic amount of p-TSA to give compound 12. The
OH
OTPS
O
a
b
c
OTHP
OTHP
3
4
5
OTPS
OTPS
OH
d
e
f
OH
OH
OH
6
7
8
O
O
OH
O
h
g
OH
O
OTBS
OTBS
OTBS
OH
9
10
11
O
O
J
i
K
O
O
O
O
O
O
OTBS
OH
13
12
O
O
O
O
O
O
L
O
O
O
HO
O
14
1
Scheme 3. Reagents and conditions: (a) HCCCH2OTHP, n-BuLi, BF3OEt, THF, ꢁ78 °C, 3 h, 75 %; (b) TBDPSCl, imidazole, cat DMAP, dry CH2Cl2, 4 h, 93%; (c) PPTS, MeOH, 0 °C to
rt, 5 h, 85%; (d) Red-Al, THF, 0 °C-rt, 12 h, 88%; (e) p-TSA, MeOH, 0 °C-rt, 6 h, 93%; (f) TBDMSCl, imidazole, dry CH2Cl2, 0 °C-rt, 4 h, 92%; (g) (Ac)2O, Py, 0 °C-rt, 3 h, 93%; (h)
ADMIX-
a
, t-BuOH: H2O (1:1), 0 °C, 24 h, 86 %; (i) 2,21-DMP, dry CH2Cl2, PTSA, 1 h, 88%; (j) TBAF, THF, 0 °C-rt, 30 min, 92 %; (k) i. IBX, dry DMSO, dry CH2Cl2, 5 h, 92%; ii.
PPh3 = CO2Et, MeOH, 0 °C, 24 h, 76.1 %; (l) 80% aq AcOH, 0 °C-rt, 24 h, 97%.

D. K. Reddy et al. / Bioorg. Med. Chem. Lett. 21 (2011) 997–1000
999
Table 1
Antibacterial activity of compound 1.
Microorganism
Minimum inhibitory concentration (MIC) (
l
g/ml)
Streptomycin
Compound 1
Penicillin-G
Nitrofurantoin
Gram positive bacteria
B. Subtilis (MTCC 441)
S. aureus (MTCC 96)
25
6.25
50
1.562
1.562
1.562
100
50
50
S. epidermides (MTCC 437)
Gram negative bacteria
E. coli (MTCC 443)
P. aeruginosa (MTCC 741)
K. pneumonia (MTCC 39)
12.5
50
50
1.562
1.562
1.562
25
100
50
Minimum inhibitory concentrations (MICs) are in lg/ml. Negative control DMSO – no activity
Note: positive controls: penicillin for Gram positive bacteria.
Streptomycin for Gram negative bacteria.
Nitrofurantoin for both microorganisms.
marized in Table 2. The antifungal activity of compound 1 was
studiedagainstR. oryzae(MTCC262), A. niger(MTCC1344), C. albican
(MTCC 227), and S. cerevisiae (MTCC 171). Compound 1 showed good
activity with zone of inhibition values in the range of 12–14 mm at a
Table 2
Antifungal activity of compound 1.
Microorganism
Zone of inhibition (mm)
Compound 1
Claotrimazole
30 lg/ml
compound concentration of 100 lg/ml against R. oryzae (MTCC 262)
Fungi
100
lg/ml
and C. albican (MTCC 227) and showed moderate activity with zone
of inhibition values in the range of 8–10 mm at a compound concen-
tration of 100 lg/ml against A. niger (MTCC 1344) and S. cerevisiae
(MTCC 171). The controls were maintained with clotrimazole for
all fungi. Zone of inhibition values for standard drug clotrimazole
for all fungi are presented in Table 2.
R. oryzae (MTCC 262)
A. Niger (MTCC 1344)
C. albicans (MTCC 227)
S. cerevisiae (MTCC 171)
14
10
12
8
21
18
22
23
Zone of inhibition diameter are in mm. Negative control DMSO – no activity
Note: positive control: claotrimazole for all fungi.
In conclusion, the synthesis of botryolide-E from propylene
oxide has been achieved employing Jacobsen’s hydrolytic kinetic
resolution (HKR), selective epoxide opening, Sharpless asymmetric
dihydroxylation, one pot acetonide deprotection and lactonization
as key steps, there by confirming the absolute configuration as 4S,
5S and 7R. Biological behavior of botryolide-E against bacteria and
fungi has been evaluated. Botryolide-E shows significant potent
tert-butyldimethylsilyl group in 12 was removed using tetrabutyl-
ammonium fluoride (TBAF) to afford alcohol 13, which was oxidized
using IBX (2-iodoxybenzoic acid) and subsequently reacted with
(ethoxycarbonylmethylene)triphenylphosphorane in dry methanol
at 0 °C for 24 h to give the Wittig product in 82% yield with a Z:E ratio
activity against S. aureus (MTCC 96) (6.25
E. coli (MTCC 443) (12.5 g/ml), B. subtilis (MTCC 441) (25
and moderate activity against S. epidermidis (MTCC 437) (50
ml), P. aeruginosa (MTCC 741) (50 g/ml) and Klebsiella pneumonia
(MTCC 39) (50 g/ml). Compound 1 exhibited good to moderate
antifungal activity.
Experimental section. General experimental procedures are
described in the Supplementary data.
l
g/ml), good against
g/ml)
g/
of 85:15. The pure
Z isomer 14 was separated by column
l
l
chromatography (Scheme 3), which was reacted with 80% aq AcOH
at room temperature for 24 h, to afford single product 1 quantitative
yield in one pot acetonide deprotection and lactonization (Scheme
3). The physical and spectral data of synthetically prepared com-
pound 15 1 (1H NMR and 13C NMR) were found to be in good agree-
l
l
l
ment the natural product8 {½a D25
ꢀ
ꢁ36.7 (c 0.05, CHCl3), lit.8
½ ꢀ
a 2D5
ꢁ38 (c 0.05, CHCl3)} there by confirming the absolute configuration
of natural product botryolide-E 1 as 4S, 5S and 7R configuration.
The in vitro biological activity of botryolide-E against bacteria
was evaluated. All the microbial culture were procured from MTCC,
IMTECH, Chandigarh, India. The antibacterialactivityof botryolide-E
1 wastestedagainsta panelofbacteriabybrothdilutionmethodrec-
ommended by National Committee for Clinical Laboratory (NCCL)
standards procedure,13 and minimum inhibitory concentrations
(MICs) are summarized in Table 1. It has been observed that the test
compound botryolide-E exhibited good antibacterial activity with
degree of variation. Natural product botryolide-E (1) exhibited sig-
Acknowledgment
The authors are thankful CSIR, New Delhi, India for the financial
support.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.12.024.
nificant potent activity against S. aureus (MTCC 96) (6.25
good activity against E. coli (MTCC 443) (12.5 g/ml) and B. subtilis
(MTCC 441) (25 g/ml) and exhibits moderate activity against S. epi-
dermidis (MTCC 437) (50 g/ml) and P. aeruginosa (MTCC 741)
(50 g/ml),K. pneumonia(MTCC39)(50 g/ml). Controlsweremain-
lg/ml),
l
References and notes
l
l
1. Klevens, R. M.; Morrison, M. A.; Nadle, J.; Petit, S.; Gershman, K.; Ray, S.;
Harrison, L. H.; Lynfield, R.; Dumyati, G.; Townes, J. M.; Craig, A. S.; Zell, E. R.;
Fosheim, G. E.; McDougal, L. K.; Carey, R. B.; Fridkin, S. K. J. Am. Med. Assoc.
2007, 298, 1763.
2. (a) Levy, S. B.; Marshall, B. Nat. Med. 2004, 10, S122; (b) Tomasz, A. N. Eng. J.
Med. 1994, 330, 1247.
3. Fridkin, S. K.; Edwards, J. R.; Courval, J. M.; Hill, H.; Tenover, F. C.; Lawton, R.;
Gaynes, R. P.; McGowan, J. E., Jr. Ann. Int. Med. 2001, 135, 175.
4. Hoffmann, H. M. R.; Rabe, J. Angew. Chem., Int. Ed. Engl. 1985, 24, 94.
5. Li, D. H.; Zhu, T. J.; Liu, H. B.; Fang, C. Y.; Gu, Q. Q.; Zhu, W. M. Arch. Pharmacol.
Res. 2006, 29, 624.
l
l
tained with DMSO and penicillin-G (for Gram positive bacteria),
streptomycin (for Gram negative bacteria) and nitrofurantoin for
all bacteria were used as positive controls, respectively. MIC values
of standard drugs penicillin-G, streptomycin and nitrofurantoin
against bacteria are provided in Table 1. Agar cup bioassay method
was employed for testing antifungal activity of compound 1 follow-
ing the standard procedure14 and zone of inhibitions (ZOIs) are sum-

1000
D. K. Reddy et al. / Bioorg. Med. Chem. Lett. 21 (2011) 997–1000
6. Cateni, F.; Zilic, J.; Zacchigna, M.; Bonivento, P.; Frausin, F.; Scarcia, V. Eur. J.
Med. Chem. 2006, 41, 192.
7. Ma, S.; Shi, Z.; Yu, Z. Tetrahedron 1999, 55, 12137.
14. (a) E. Margery Linday, Practical Introduction to Microbiology; E. & F.N. Spon: UK,
1962, p 177.; (b) Ref. 13b.
15. Spectral data for selected compounds: Compound 11: ½a D25
ꢀ
: ꢁ39.5 (c 0.25, CHCl3).
8. Sy, A. A.; Swenson, D. C.; Gloer, J. B.; Wicklow, D. T. J. Nat. Prod. 2008, 71, 415.
9. (a) Kumar Reddy, D.; Shekhar, V.; Srikanth Reddy, T.; Purushotham Reddy, S.;
Venkateswarlu, Y. Tetrahedron: Asymmetry 2009, 20, 2315; (b) Shekhar, V.;
Kumar Reddy, D.; Suresh, V.; Chanti Babu, D.; Venkateswarlu, Y. Tetrahedron
Lett. 2010, 51, 946; (c) Prabhakar, P.; Rajaram, S.; Kumar Reddy, D.; Shekar, V.;
Venkateswarlu, Y. Tetrahedron: Asymmetry 2010, 21, 216.
10. Schaus, S. E.; Brandes, B. D.; Larrow, J. F.; Tokunaga, M.; Hansen, K. B.; Gould, A.
E.; Furrow, M. E.; Jacobsen, E. N. J. Am. Chem. Soc. 2002, 124, 1307.
11. Yadav, J. S.; Reddy, P. M. K.; Gupta, M. K.; Chary, C. J. Synthesis 2007, 23, 3639.
12. Kolb, H. C.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483.
13. (a) National Committee for Clinical Laboratory Standards (NCCLS), Standard
Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria, Which Grows
Aerobically; Nat. Comm Clini. Lab. Stands: Villanova, 1982, p 242.; (b) Kumar
Reddy, D.; Shekhar, V.; Prabhakar, P.; Chinna Babu, B.; Siddhardha, B.; Murthy,
U. S. N.; Venkateswarlu, Y. Eur. J. Med. Chem. 2010, 45, 4657.
IR (Neat): t .
3435, 2925, 1716, 1643, 1378, 1267 cmꢁ1 1H NMR (300 MHz,
CDCl3): d 5.12 (ddq, J = 12.1, 6.8, 4.2 Hz, 1H), 3.67 (dd, J = 5.0, 2.4 Hz, 2H), 3.64–
3.60 (m, 1H), 3.42–3.24 (m, 1H) 3.07 (br s, OH), 2.63 (br s, OH), 2.04 (s, 3H),
1.76 (ddd, J = 14.1, 11.1, 3.0 Hz, 1H), 1.62 (ddd, J = 14.3, 10.0, 2.8 Hz, 1H), 1.28
(d, J = 6.2 Hz, 3H), 0.9 (s, 9H), 0.08 (s, 6H). 13C NMR (75 MHz, CDCl3): d 170.6,
67.8, 67.6, 66.9, 39.9, 29.9, 29.5, 25.6, 21.2, 19.4, ꢁ2.9, ꢁ3.6. ESIMS: m/z 329
[M + Na]+.
Compound 1: ½a 2D5
ꢀ : ꢁ36.7 (c 0.05, CHCl3). IR (Neat): t 3424, 2924, 2854, 1725,
1739, 1663, 1250.cmꢁ1.1H NMR (300 MHz, CDCl3): d 7.45 (dd, 1H, J = 6.0,
1.5 Hz), 6.20 (dd, 1H, J = 6 0, 1.5 Hz), 5.13–5.08 (m, 1H), 5.05–5.01 (m, 1H),
3.88–3.85 (m, 1H), 3.23 (br s, OH), 2.04 (S, 3H), 1.72–1.81 (m, 2H), 1.27 (d, 3H,
J = 6.3 Hz). 13C NMR (75 MHz, CDCl3): d 172.8, 172.0, 153.4, 123.0, 85.0, 67.6,
67.3, 39.1, 21.2, 20.6. ESIMS: m/z 214 [M]+.