OSW Saponins: Facile synthesis toward a new type of structures with potent antitumor activities

Article abstract of DOI:10.1021/jo051536b

OSW saponins, featuring a 16β,17α-dihydroxycholest-22-one aglycon and an acylated β-D-xylopyranosyl-(1→3)-α-L- arabinopyranosyl residue attached to the 16-hydroxyl group, have recently been discovered from a group of lily plants, which show potent antitumor activities with a novel mechanism of action. This paper describes an aldol approach to the stereoselective construction of the 16α,17α-dihydroxycholest-22-one structure from 16α-hydroxy-5-androsten-17-ones and propionates. Elaboration of the aldol adducts toward OSW-1, involving installation of the isoamyl ketone side chain, inversion of the 16-hydroxyl configuration, and selective protection of the C22-oxy function, has been explored and accomplished. In particular, the present route was found convenient for the synthesis of OSW saponin analogues with a C22-ester side chain. Thus, the 23-oxa-analogue of OSW-1 (40) was prepared starting from the industrial dehydroisoandrosterone (1) in a linear eight-step sequence and in 26% overall yield. Analogues with a variety of modified side chains were prepared, via aldol condensation with propionates of varying length, thiopropionate, and acetate (for preparation of 68-75) or via aminolysis of the 22,16-lactone 26 (for preparation of the 23-N-analogues). Cross metathesis (CM) reaction was also found feasible for modification at the final stage from C22-allyl ester 70. Valuable structure-activity relationships (SAE), together with the practical synthetic approach, have thus been provided to set a new stage for further studies on this new type of antitumor structures.

Full text of DOI:10.1021/jo051536b

OSW Saponins: Facile Synthesis toward a New Type of Structures
with Potent Antitumor Activities
Bingfeng Shi,† Pingping Tang,† Xiaoyi Hu,‡ Jun O. Liu,‡ and Biao Yu*,†
State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, and Departments
of Pharmacology and Neuroscience, Johns Hopkins School of Medicine, 725 North Wolfe Street,
Baltimore, Maryland 21205
byu@mail.sioc.ac.cn
Received July 23, 2005
OSW saponins, featuring a 16â,17R-dihydroxycholest-22-one aglycon and an acylated â-D-
xylopyranosyl-(1f3)-R-L-arabinopyranosyl residue attached to the 16-hydroxyl group, have recently
been discovered from a group of lily plants, which show potent antitumor activities with a novel
mechanism of action. This paper describes an aldol approach to the stereoselective construction of
the 16R,17R-dihydroxycholest-22-one structure from 16R-hydroxy-5-androsten-17-ones and propi-
onates. Elaboration of the aldol adducts toward OSW-1, involving installation of the isoamyl ketone
side chain, inversion of the 16-hydroxyl configuration, and selective protection of the C22-oxy
function, has been explored and accomplished. In particular, the present route was found convenient
for the synthesis of OSW saponin analogues with a C22-ester side chain. Thus, the 23-oxa-analogue
of OSW-1 (40) was prepared starting from the industrial dehydroisoandrosterone (1) in a linear
eight-step sequence and in 26% overall yield. Analogues with a variety of modified side chains
were prepared, via aldol condensation with propionates of varying length, thiopropionate, and
acetate (for preparation of 68-75) or via aminolysis of the 22,16-lactone 26 (for preparation of the
23-N-analogues). Cross metathesis (CM) reaction was also found feasible for modification at the
final stage from C22-allyl ester 70. Valuable structure-activity relationships (SAR), together with
the practical synthetic approach, have thus been provided to set a new stage for further studies on
this new type of antitumor structures.
Introduction
con and an acylated â-D-xylopyranosyl-(1f3)-R-L-ara-
binopyranosyl residue attached to the 16-hydroxyl group
(Figure 1), were found, in 1995, to possess extremely
potent cytotoxicity toward leukemia HL-60 cells with IC50
values ranging between 0.1 and 0.3 nM.2 The major
constituent, namely, OSW-1, was then tested against the
NCI (U.S. National Cancer Institute) 60 cell lines,
In 1992, Sashida, Mimaki, and co-workers1 reported a
new type of cholestane glycosides from the bulbs of
Ornithogalum saudersiae, a perennial garden plant of the
lily family cultivated in southern Africa. These saponins,
featuring a novel 16â,17R-dihydroxycholest-22-one agly-
* Corresponding author: fax (0086)-21-64166128.
† Shanghai Institute of Organic Chemistry.
(2) (a) Mimaki, Y.; Kuroda, M.; Kameyama, A.; Sashida, Y.; Hirano,
T.; Oka, K.; Maekawa, R.; Wada, T.; Sugita, K.; Beutler, J. A. Bioorg.
Med. Chem. Lett. 1997, 7, 633. (b) Rouhi, A. M. Chem. Eng. News 1995,
September 11, 28.
‡ Johns Hopkins School of Medicine.
(1) Kubo, S.; Mimaki, Y.; Terao, M.; Sashida, Y.; Nikaido, T.;
Ohmoto, T. Phytochemistry 1992, 31, 3969.
10.1021/jo051536b CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/05/2005
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J. Org. Chem. 2005, 70, 10354-10367

OSW Saponins with Potent Antitumor Activities
3â-ol-17-one via a sequence of Wittig olefination and ene
reaction and then introduced the 16â,17R-diol by dihy-
droxylation (of the 16,17-ene with 1 equiv of OsO4)
followed by inversion of the resulting 16R-OH. Shortly
thereafter, we succeeded in coupling of a suitably pro-
tected aglycon with a disaccharide trichloroacetimidate
to complete the first total synthesis of OSW-1.6 Yu and
Jin7 have then improved the synthesis by introducing the
side chain via a 1,4-addition of a 17(20)-en-16-one with
an R-alkoxy vinyl cuprate, followed by the elaboration of
the 17R-OH by oxidation of the resulting 16,17-enolate
with Davis reagent. Morzycki et al.8 realized an intramo-
lecular ring opening of the 16R,17R-epoxide by the C22-
carbonyl function to start further elaboration.
Although these developments have allowed access to
the natural OSW-1 saponin and its analogues, the
existing syntheses are time-consuming and require subtle
control of the reaction conditions for some of the trans-
formations. As a result, only a limited number of OSW
saponin analogues have been obtained by means of
chemical synthesis for SAR studies. Nevertheless, several
key structural elements in OSW saponins essential for
their activity have been identified. It was shown that
either the aglycon analogues10 or the disaccharide deriva-
tives (bearing disparate steroidal aglycons)11 were nearly
inactive toward tumor cells. The C16-epimer of OSW-1
was also inactive.12 In contrast, saturation of the C5-
C6 double bond13 and dimerization with a terephthalic
acid at the 3-OH did not affect significantly the antitumor
activity.12 And the C17-side chain can tolerate modifica-
tion, for example, reduction of the C22-carbonyl function
into CH2 or removal of the terminal CH3, without
apparently changing the antitumor potency.14
Thus, a stage has been set for altering the nature of
the synthetic challenge from total synthesis of the natural
compounds or random preparation of their analogues to
the preparation of a variety of targeted analogues and
derivatives to extend the SAR profile and to study the
mechanism of action of OSW saponins. Another goal is
to find a lead compound that could be prepared in
multigram quantities for toxicological and pharmacoki-
netic studies. In fact, we have recently developed an
efficient aldol approach to the construction of the 16R,-
17R-dihydroxycholest-22-one structure, which can be
converted to the 23-oxa analogues of OSW saponins
conveniently. And importantly, these C17 side-chain-
modified 23-oxa analogues were found to be as potent as
the parent natural products against the growth of tumor
cells.15 Herein, we report a comprehensive account on this
matter.
FIGURE 1. Naturally occurring OSW saponins.
showing a mean IC50 of 0.78 nM, which is 10-100 times
more potent than those of the clinically applied antican-
cer agents such as mitomycin C, adriamycin, cisplatin,
camptothecin, and taxol. Moreover, OSW-1 demonstrated
little toxicity toward normal human pulmonary cells in
vitro and prolonged the life span of mice injected with
the P388 leukemia cell line by 59% via a single admin-
istration of 10 µg/kg.2a Also intriguing is that OSW-1
showed equal potency against tumor cells resistant to
other anticancer agents and displayed a characteristic
antitumor profile that is only comparable to those of the
cephalostatins.2a,3 These results imply a new anticancer
mechanism underlying the action of this new type of
natural products.
Continuous search in O. saudersiae and its taxonomi-
cally related plants, for example, Ornithogalum thyr-
soides and Galtonia candicans, has led to the identifica-
tion of some 20 more OSW saponins (Figure 1).4 Thus a
preliminary set of SAR (structure-activity relationship)
information has been obtained: (1) The acyl groups on
the disaccharide segment (R1 and R2) are crucial to the
antitumor activity of the molecules; lack of the R2
methoxybenzoyl or (E)-cinnamoyl substitution reduces
the activity by ∼100 fold, while removal of both R1
(acetyl) and R2 reduces the activity by ∼1000-fold. (2) An
additional â-D-glucopyranosyl residue (R3) on the disac-
charide reduces the antitumor activity by ∼100 fold. (3)
Presence of a â-D-glucopyranosyl residue at the 3-OH (R4)
does not affect the activity; but a di- or trisaccharide R4
substitution diminishes the activity by more than 1000-
fold.
Synthetic efforts have been made toward OSW sa-
ponins since the discovery of their potent antitumor
activities.5-9 Notably, Guo and Fuchs5 achieved the first
synthesis of the 16â,17R-dihydroxycholest-22-one aglycon
in 1998. They assembled the side chain onto 5-androsten-
(9) For other efforts toward the synthesis of OSW saponins, see (a)
Morzycki, J. W.; Gryszkiewicz, A. Pol. J. Chem. 2001, 75, 983. (b)
Morzycki, J. W.; Gryszkiewicz, A. Jastrzebska, I. Tetrahedron 2001,
57, 2185. (c) Morzycki, J. W.; Wojtkielewicz, A.; Gryszkiewicz, A.;
Wolczynski, S. Bioorg. Med. Chem. Lett. 2004, 14, 3323. (d) Xu, Q.;
Peng, X.; Tian, W. Tetrahedron Lett. 2003, 44, 9375.
(10) Guo, C.; LaCour, T. G.; Fuchs, P. L. Bioorg. Med. Chem. Lett.
1999, 9, 419.
(3) For the GI50, TGI, and LC50 values of OSW-1 against the NCI
60 cell-line tumor panel, see the Supporting Information in ref 4c.
(4) (a) Kuroda, M.; Mimaki, Y.; Yokosuka, A.; Hasegawa, F.; Sashida,
Y. J. Nat. Prod. 2002, 65, 1417. (b) Kuroda, M.; Mimaki, Y.; Yokosuka,
A.; Sashida, Y. Chem. Pharm. Bull. 2001, 49, 1042. (c) Kuroda, M.;
Mimaki, Y.; Yokosuka, A.; Sashida, Y.; Beutler, J. A. J. Nat. Prod.
2001, 64, 88.
(5) Guo, C.; Fuchs, P. L. Tetrahedron Lett. 1998, 39, 1099.
(6) Deng, S.; Yu, B.; Lou, Y.; Hui, Y. J. Org. Chem. 1999, 64, 202.
(7) (a) Yu, W.; Jin, Z. J. Am. Chem. Soc. 2001, 123, 3369. (b) Yu,
W.; Jin, Z. J. Am. Chem. Soc. 2002, 124, 6576.
(8) (a) Morzycki, J. W.; Gryszkiewicz, A.; Jastrzebska, I. Tetrahedron
Lett. 2000, 41, 3751. (b) Morzycki, J. W.; Wojtkielewicz, A. Carbohydr.
Res. 2002, 337, 1269.
(11) (a) Ma, X.; Yu, B.; Hui, Y.; Miao, Z.; Ding, J. Carbohydr. Res.
2000, 329, 495. (b) Ma, X.; Yu, B.; Hui, Y.; Miao, Z.; Ding, J. Carbohydr.
Res. 2001, 334, 159.
(12) Ma, X.; Yu, B.; Hui, Y.; Miao, Z.; Ding, J. Bioorg. Med. Chem.
Lett. 2001, 11, 2153.
(13) Deng, L.; Wu, H.; Yu, B.; Jiang, M.; Wu, J. Chin. J. Chem. 2004,
22, 994.
(14) Deng, L.; Wu, H.; Yu, B.; Jiang, M.; Wu, J. Bioorg. Med. Chem.
Lett. 2004, 14, 2781.
J. Org. Chem, Vol. 70, No. 25, 2005 10355

Shi et al.
ment (leading to the corresponding 17â-hydroxy-16-oxo
steroids) was not detected.20 Blocking the 16R-OH of 5
with TBS ether provided 7.
We first examined the aldol condensation of ketones
5-7 with lithium E-enolate of ethyl propionate, which
was generated with solid lithium diisopropylamide (LDA)
in 23% hexamethylphosphoric triamide (HMPA)-tet-
rahydrofuran (THF) via the method of Ireland (conditions
A, Figure 4),21 where the highest percentage of the E
isomer resulted from rapid addition of a slight excess
(1.05-1.10 equiv) of the ester neat to a solution of the
base.21b,c,22 As expected, only the 17R-hydroxy(silyloxy)-
20S- products 8a, 9a, and 10a were isolated (in 41%, 63%,
and 43% yield, respectively) (entries 1-3). Blocking the
neighboring 16R-OH was proven unnecessary for the
present aldol condensation. For steric reasons the trans-
fused five-membered 20,16-lactone could not be pro-
duced.18,23 Without control of the exclusive generation of
the E-enolate of ethyl propionate (conditions B, without
use of hexane-free LDA), reaction of ketone 5 provided
the desired 20S product 8a in a comparable 41% yield,
but its 20R isomer 8b was also isolated in 29% yield
(entry 4). However, reaction of the 3-O-TBS-17-ketone 6
under similar conditions in the absence of HMPA (condi-
tions C) afforded the desired 9a in a satisfactory 75%
yield, with its 20R isomer 9b being isolated in only 12%
yield (entry 5). Interestingly, under the relatively con-
venient conditions C, condensation of 6 with isobutyl and
dodecyl propionate provided the desired 17R-hydroxy-20S
adducts 11a and 12a in good yields (78% and 81% yield,
respectively); their 20R products were not isolated (en-
tries 6 and 7). The predominant formation of the 20S
isomers under conditions B and C could be explained by
the following rationale: upon addition of a trapping agent
such as excess esters, a kinetic resolution process led
through preferential destruction of the (Z)-lithium eno-
late to a relative increase of the amount of the (E)-lithium
enolate formed;21b,24 and with the E-enolate preferred in
the aldol reaction, the thermodynamic equilibrium for
(E)- to (Z)-enolate was expedited. The increased domi-
nance of the E-enolates in the reaction conditions due to
the increased size of the isobutyl and dodecyl group
(compared to that of the ethyl group) was somewhat
responsible for the latter results.25
FIGURE 2. Proposed stereochemistry in the aldol approach
to the construction of the cholestane 20(S)-16R,17R-diol struc-
ture.
Results and Discussion
Aldol Approach to the Cholestane 16R,17R-Dihy-
droxy-22-one Structure. A major challenge in the
synthesis of OSW saponins has been the construction of
the 16â,17R-dihydroxycholest-22-one structure.5-9 When
this synthetic target is envisioned to be a R-methyl-â,γ-
diol-one, an aldol condensation between an R-hydroxyke-
tone and a propionate could be the direct approach.16
Then the challenge lies in the stereo control of the aldol
reaction to place the 21-methyl and 17-hydroxyl groups
in S(C20) and R orientations, respectively. We anticipated
that condensation with a 16R-hydroxy-17-ketone steroi-
dal substrate could lead to the formation of the desired
stereochemistry at C-17 and C-20, considering the 16R-
OR group could force the approach of the enolate from
the â face via intermediate I (Figure 2) in a nonchelation
model,17 and the chair transition state (in a Zimmerman-
Traxler model)17a could prefer the E- to the Z-enolate to
avoid the interaction of the 18-methyl group and the
methyl of the propionate enolate (intermediate II). Al-
though it has long been known that zinc enolates of
propionates under the Reformatsky conditions approached
the 16R-acetoxy-17-oxo-androstanes from the R face,18
encouraging results have been provided by Doller and
Gros19 that lithium enolate of tert-butyl propionate
proceeded by a â-face attack.
The required 16R-hydroxy-5-androsten-17-one deriva-
tives 5 and 6, with their 3-OH being protected with a
robust TBDPS (tert-butyldiphenylsilyl) and a TBS (tert-
butyldimethylsilyl) ether, respectively, were readily pre-
pared from the industrial acetate 1 following modification
of a literature procedure (Figure 3).20 Thus, bromination
of ketone 1 with 3 equiv of CuBr2 in methanol under
reflux provided 16R-bromide 2 in 91% yield, with the 3-O-
acetyl group being fully cleaved. Protection of the 3-OH
with TBDPSCl or TBSCl in the presence of imidazole in
N,N-dimethylformamide (DMF) gave 3 and 4. Epimer-
ization between the 16R-bromide and its 16â isomer took
place readily under alkaline conditions, where they were
subjected to SN2 displacement with hydroxy ion, leading
stereospecifically (from the 16â-bromides only) to the 16R-
ols 5 and 6 in 95% yields. The reported ketol rearrange-
The C17 ester chain was assigned as â-oriented in the
aldol adducts 8a-12a, that is, trans to the 16R-OH,
because otherwise the corresponding 16,22-γ-lactone
would be readily formed in the presence of mineral
acids.18 Direct evidence was provided by the ready
formation of the 16,17-O-acetonide 13 from diol 8a
(Figure 5).
At this stage, however, the stereochemistry at C20 in
the aldol adducts could not be established definitely.
Analysis of the chair transition state (Figure 2) and
(15) Shi, B.; Wu, H.; Yu, B.; Wu, J. Angew. Chem., Int. Ed. 2004,
43, 4324.
(16) Reetz, M. T. Angew. Chem., Int. Ed. Engl. 1984, 23, 556.
(17) (a) Zimmerman, H. E.; Traxler, M. D. J. Am. Chem. Soc. 1957,
79, 1920. (b) Kleschick, W. A.; Buse, C. T.; Heathcock, C. H. J. Am.
Chem. Soc. 1977, 99, 247. (c) Evans, D. A. Top. Stereochem. 1982, 13,
1.
(18) Mazur, Y.; Danieli, N.; Sondheimer, F. J. Am. Chem. Soc. 1960,
82, 5889.
(19) Doller, D.; Gros, E. G. Synth. Commun. 1990, 20, 3115.
(20) Numazawa, M.; Nagaoka, M.; Osawa, Y. J. Org. Chem. 1982,
47, 4024.
(21) (a) Ireland, R. E.; Mueller, R. H. J. Am. Chem. Soc. 1976, 98,
2891. (b) Ireland, R. E.; Wipf, P.; Armstrong, J. D., III J. Org. Chem.
1991, 56, 650. (c) Oare, D. A.; Heathcock, C. H. J. Org. Chem. 1990,
55, 157.
(22) Corey, E. J.; Gross, A. W. Tetrahedron Lett. 1984, 25, 495.
(23) Grigsby, W. E.; Hind, J.; Chanley, J.; Westheimer, F. H. J. Am.
Chem. Soc. 1942, 64, 2606.
(24) Heathcock, C. H. In Asymmetric Synthesis; Morrison, J. D., Ed.;
Academic Press: Orlando, FL, 1984; Vol. 3, p 111 and references
therein.
(25) Otera, J.; Fujita, Y.; Fukuzumi, S. Synlett 1994, 213.
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OSW Saponins with Potent Antitumor Activities
FIGURE 3. Introduction of the 16R-OH.
tion of the natural 20S isomers as the major products.18,26
These assignments were later confirmed unambiguously
by NOE correlation and X-ray diffraction analysis of the
transformed compounds. Upon comparison of the 1H
NMR spectra of the pair of the 20S and 20R isomers, the
21-methyl signal of the 20S isomers was observed at a
relatively lower field, that is, 1.26 and 1.29 ppm, respec-
tively, for the 21-methyl protons in the 20S isomers 8a
and 9a versus 1.30 and 1.32 ppm in the 20R isomers 8b
and 9b. A similar chemical shift differentiation has been
found in steroids unsaturated at the 16(17) position,27
while an opposite trend was found in steroids saturated
at the 16(17) position.28
Elaboration of the Cholestane Isoamyl Ketone
Side Chain. Starting from the 22-esters 8a and 10a, we
first tried to install the isoamyl residue on the cholestane
side chain via addition to the corresponding Weinreb
amides.29 Unexpectedly, preparation of the desired Wein-
reb amides from the 22-esters was found to be difficult
(Figure 6). Under the action of Et2AlCl (conditions A;
AlMe330 or Me2AlCl31 is usually used, but these reagents
were not accessible to us), reaction of ester 10a with Me-
(MeO)NH‚HCl did not produce the desired amide; in-
stead, the 21-methyl epimerized compound 10b was
isolated as the only product (53%, entry 1). Ester 8a
remained intact under similar conditions. We then
examined Merck’s conditions with i-PrMgCl as a pro-
moter (conditions B) for the amide formation.32 Modified
conditions with an excess amount of isoamylmagnesium
chloride instead (conditions C) were also examined; thus
an in situ addition to the newly formed Weinreb amide
might take place to provide the desired cholestane
directly.32 Ester 10a with its 16R-OH being blocked was
inert toward these conditions. Fortunately, the 16R-OH
unprotected 8a was readily converted into amide 14 in
75% yield in the presence of i-PrMgCl (entry 4).
FIGURE 4. Aldol condensation with propionate enolates.
(26) (a) Oka, K.; Hara, S. J. Org. Chem. 1978, 43, 4408. (b) Lardon,
A.; Reichstein, T. Helv. Chim. Acta 1941, 24, 1127. (c) Hey, D. H.;
Honeyman, J.; Peal, W. J. J. Chem. Soc. 1954, 185, 2648.
(27) (a) Marino, J. P.; Abe, H. J. Am. Chem. Soc. 1981, 103, 2907.
(b) Schmuff, N. R.; Trost, B. M. J. Org. Chem. 1983, 48, 1404.
(28) (a) Piatak, D. M.; Wicha, J. Chem. Rev. 1978, 78, 199. (b) Ibuka,
T.; Taga, T. J. Org. Chem. 1988, 53, 3947. (c) Nes, W. R.; Varkey, T.
E.; Krevitz, K. J. Am. Chem. Soc. 1977, 99, 260.
(29) Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815.
(30) (a) Basha, A.; Lipton, M.; Weinreb, S. M. Tetrahedron Lett.
1977, 18, 4171. (b) Levin, J. I.; Turos, E.; Weinreb, S. M. Synth.
Commun. 1982, 12, 989.
FIGURE 5. Formation of the 16,17-O-acetonide 13.
(31) Shimizu, T.; Osako, K.; Nakata, T. Tetrahedron Lett. 1997, 38,
2685.
inspection of the literature results on addition of steroidal
17-ones with ethyl R-bromo(iodo)-propionates under Re-
formatsky conditions concluded favorably to the forma-
(32) Williams, J. M.; Jobson, R. B.; Yasuda, N.; Marchesini, G.
Dolling, U.-.; Grabowski, E. J. J. Tetrahedron Lett. 1995, 36, 5461.
J. Org. Chem, Vol. 70, No. 25, 2005 10357

Shi et al.
FIGURE 8. Alkylation of 22-ethyl ester 8a.
hindrance at the C22-carbonyl carbon of Weinreb amide
14. The production of the demethoxylation derivatives
(e.g., 18 and 19) from Weinreb amides in the presence of
a strong base has been previously observed.33,34 An E2
pathway was postulated; thus the basicity of the alky-
lation agents prevailed to effect abstraction of a proton
from the N-methoxy group, leading to amide derivatives
such as 18 and 19. It should also be noted that the above
alkylation reactions had to be quenched by pouring into
a cold 5% HCl solution, otherwise the corresponding
retro-aldol product 5 was produced.
FIGURE 6. Preparation of the Weinreb amides.
In view of the hindrance of the C22-carbonyl function
in the above experiments, we rationalized that alkylation
of the 22-esters (instead of the bulkier Weinreb amides)
would proceed much more easily, and overaddition to the
ketone products could not take place at all. Thus similar
conditions as described above for alkylation of the Wein-
reb amide 14 were then applied to ethyl ester 8a (Figure
8). Encouragingly, reaction of ester 8a with MeLi and
n-BuLi gave the corresponding ketones 15 and 16 in good
yields (69% and 58%, respectively). However, alkylation
with isoamyllithium led to the isoamyl ketone 17 in only
moderate yield (34%). Byproducts were then carefully
isolated and identified to explain the alkylation processes.
Overalkylation on ketone 17 took place, providing 22-ol
20 (17%). Retro-aldol reaction of the substrate ester 8a
also proceeded, leading to ketone 5. Alkylation of 5
afforded a pair of the 17R/â-ol isomers 21 (19%) and 22
(6%). The presence of 21 and 22 demonstrated that the
retro-aldol reaction took place before the reaction was
quenched. It was also noticed that the â-face addition of
the lithium reagent onto the 16R-hydroxy-17-one 5 was
favored over the R-face addition, leading to a 21:22 ratio
of ∼3:1; while the previous aldol addition with lithium
enolate of ethyl propionates effected exclusive â-face
addition.
FIGURE 7. Alkylation of Weinreb amide14.
These experimental results for the preparation of
Weinreb amides implied that the C22-carbonyl carbon
in the 16R,17R-dihydroxy steroidal structure was steri-
cally very hindered. Therefore, it was not surprising that
alkylation of 22-amide 14 with Grignard reagents, that
is, isoamylmagnesium chloride, did not proceed at all.
Then we tried substitution with alkyllithium reagents
(Figure 7). Alkylation of amide 14 with MeLi in the
presence of TMEDA in THF at -10 °C afforded the
desired methyl ketone 15 as the major product (51%).
When the bulkier n-BuLi was employed, the correspond-
ing butyl ketone 16 was obtained in only 12% yield, while
considerable amounts of the amide derivatives 18 and
19 were produced (in 27% and 38% yield, respectively).
The reaction with isoamyllithium afforded the ketone
product 17 in a decent 40% yield, although 18 and 19
were also isolated in comparable amounts (22% and 32%
yield, respectively). These results proved the steric
We have also attempted to attach the isoamyl residue
via umpolung of the C22-carbonyl carbon (Figure 9).
(33) Graham, S. L.; Scholz, T. H. Tetrahedron Lett. 1990, 31, 6269.
(34) (a) Sibi, M. P.; Sharma, R.; Paulson, K. L. Tetrahedron Lett.
1992, 33, 1941. (b) Sibi, M. P.; Marvin, M.; Sharma, R. J. Org. Chem.
1995, 60, 5016.
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OSW Saponins with Potent Antitumor Activities
required us to quench the reaction at low temperature
(-40 to -78 °C) to obtained the desired diol 27 (76%).
Both lactone 26 and ester 27 could be converted into
hemiketal 28 quantitatively upon addition of isoamyl-
lithium. However, an attempt to reduce hemiketal 28 into
16,17,22-triol 30 with LiAlH4 (or HLiBEt3) in THF led
only to the furan derivative 29 formed via elimination of
two molecules of water.5,9b Fortunately, this problem was
solved by replacement of the THF solvent with Et2O.9a
Thus, reduction of 28 with LiAlH4 in Et2O afforded triol
30 in a good 87% yield.
In line with our expectation, treatment of triol 30 with
3 equiv of AZMBCl [2-(azidomethyl)benzoyl chloride] in
the presence of 4-(N,N-dimethylamino)pyridine (DMAP)
in THF afforded the 22-O-AZMB product 31 mainly in
48% yield.37 The 16â-O-AZMB product 32 was isolated
in 7% yield, and the corresponding 16,22-di-O-AZMB
product was not isolated (Figure 11). Glycosylation of
16â,17R-diol 31 with the disaccharide trichloroacetimi-
date 33 by use of TMSOTf as a promoter in the presence
of 4 Å molecular sieve at -20 °C afforded the desired
glycoside 34 in 61% yield.6 Then, the 22-O-AZMB group
was selectively removed with PBu3, providing 22-ol 35
in a good 82% yield. Subsequent oxidation of the resulting
22-OH with PDC afforded ketone 36 in 97% yield.
Finally, the silyl groups on 36 were removed with Pd-
(MeCN)2Cl2 in acetone-water, furnishing OSW-1 in 82%
yield.
Synthesis of OSW Saponin Analogues with Modi-
fied Side Chains. We have recently found that the C17-
side chain of OSW saponins was tolerant toward certain
modifications without a significantly effect on the anti-
tumor potency of the compounds.14 The present approach
to the synthesis of the steroidal 16â,17R-hydroxyl-22-
ester structure, for example, 27, could allow us to prepare
very easily those OSW saponin analogues with a variety
of modifications on the side chain. Our first target was
the 23-oxa analogue of OSW-1 40 (Figure 12), which has
a C22-isobutyl ester in place of the isoamyl ketone in
OSW-1. This minimal modification, that is, replacement
of the CH2 with an oxygen at the 23 position, would lead
to a clear implication on SAR. Thus, a new stage would
be set for further SAR study via analogue synthesis.
Starting from the aldol condensation product 11a, prepa-
ration of the desired 23-oxa-OSW-1 40 was straightfor-
ward, involving only four steps of reaction that have
already been examined in the synthesis of OSW-1 (Figure
11). Thus, the 16R-OH on 11a was reversed following the
sequence of oxidation with TPAP/NMO and reduction
with NaBH4/CeCl3, giving 16â-ol 38. Glycosylation of
16â,17R-diol 38 with disaccharide trichloroacetimidate
33 under the action of TMSOTf provided glycoside 39.
Final removal of the silyl groups with Pd(MeCN)2Cl2 led
to the desired 40. Remarkably, such a synthetic approach
to the 23-oxa-analogue of OSW-1 40 requires only eight
linear steps (in 26% overall yield) starting from the
industrial isoandrosterone 1.
FIGURE 9. Attempt to extend the steroidal side chain via
an umpolung approach.
Thus, the Weinreb amide 14 at hand was subjected to
reduction with 4 equiv of diisobutylaluminum hydride
(DIBAL-H) at -78 °C to produce the 22-aldehyde 23.
Again, the C22-carbonyl was resistant to reaction, lead-
ing to 23 in no more than 15% yield, with ∼58% of the
starting amide being recovered. Aldehyde 23 was then
readily transformed into 1,3-dithiane 24 in 87% yield.
Unfortunately, generation of the R-thioacetal anion with
super base n-BuLi/t-BuOK,35 followed by quenching with
methyl iodide, did not give any product. Yu and Jin7b
have previously demonstrated that generation of the
R-anion of a 16â,17R-hydroxy-22-S,S′-diphenyl acetal was
effected by n-BuLi/t-BuOK, but substitution of the anion
onto methyl iodide was not successful.
Completion of the Total Synthesis of OSW-1.
Reversion of the configuration of the 16R-hydroxyl group
on the cholestane 16R,17R-dihydroxy-22-one structure
required a sequence of oxidation (into the 16-ketone) and
reduction,5,6 thus the C22-carbonyl group needed to be
blocked first. In fact, protection of the C22-carbonyl on
17 with an ethylene glycol would furnish a formal total
synthesis of OSW-1.6 Again, such an effort on the C22-
carbonyl was proven futile. In comparison to the previous
synthesis, where a 16,17-ene-22-one was readily con-
verted into its C22-ketal, the presence of the 16R,17R-
dihydroxyl groups (in 17) should be the reason causing
the inertness of the C22-carbonyl group.
We noticed that preferential benzylation8b and silyla-
tion9a on the 22-OH could be achieved on a cholestane
16â,17R,22-triol. Thus, starting from the 3-O-TBS-22-
ester 9a, we attempted to reverse the configuration of
the 16R-hydroxyl group before introducing the isoamyl
residue on the side chain (Figure 10). Treatment of diol
9a with TPAP (tetrapropylammonium perruthenate) and
NMO (N-methylmorpholine N-oxide) in the presence of
4 Å molecular sieve gave C16-ketone 25 in 93% yield.36
The present protocol has recently been proven superior
to Swern oxidation for oxidation of the steroidal 16R-
OH.14 Reduction of ketone 25 with NaBH4/CeCl3 led
stereoselectively to 16â,17R-diol 27. However, when this
reaction was quenched at room temperature with addi-
tion of methanol and water, only the intramolecular
lactonization product 26 could be isolated (92%). This
As expected, the readily synthesized 23-oxa analogue
40 showed strong activity against the growth of tumor
cells (Table 1). Therefore, we set about our synthesis of
(35) Schlosser, M.; Strunk, S. Tetrahedron Lett. 1984, 25, 741.
(36) Paquette, L. A.; Wang, H.; Zhao, M. J. Am. Chem. Soc. 1998,
120, 5213.
(37) (a) Wada, T.; Ohkubo, A.; Mochizuki, A.; Sekine, M. Tetrahedron
Lett. 2001, 42, 1069. (b) Love, K. R.; Andrade, R. B.; Seeberger, P. H.
J. Org. Chem. 2001, 66, 8165.
J. Org. Chem, Vol. 70, No. 25, 2005 10359

Shi et al.
FIGURE 10. Conversion of the 16R-hydroxyl configuration.
FIGURE 11. Completion of the total synthesis of OSW-1.
a variety of the analogues based on the structure of 40
to decipher the influence of the side chain on the
antitumor activity of the OSW saponins (Figure 13).
Employing the aldol condensation of 3-O-TBS-16R-
hydroxy-5-androsten-17-one 6 with ethyl, isobutyl, and
dodecyl propionates, we have already obtained the C22-
ethyl ester 9a and its 20R epimer 9b, isobutyl ester 11a,
and dodecyl ester 12a (Figure 4). Under similar condi-
tions, aldol condensation of 6 with allyl, heptyl, and
octadecyl propionates provided the corresponding esters
41-43, which were applied directly to oxidation with
TPAP/NMO, affording ketones 47, 48, and 50, respec-
tively (Figure 13). At this stage, the corresponding 20R
epimers resulting from the aldol condensation could be
easily separated by silica gel column chromatograph.
Allyl and heptyl esters 47 and 48 were so obtained in
good yields (55% and 60% yield, respectively, for two
steps); their 20R epimers were isolated in 8% and 5%
yields, respectively. However, the longer octadecyl ester
50 was obtained in only a moderate yield of 32%; while
its 20R epimer was obtained in 22% yield. This might be
due to the poor solubility of the octadecyl propionate in
the aldol reaction at low temperature. Detection of
octadecyl alcohol in the reaction mixture indicated that
esterolysis might be another reason. It should also be
mentioned that once we scaled up the aldol condensation
of 6 with dodecyl propionate at a 2.0 g scale, after
oxidation, the desired 20S ester 49 was obtained in 51%
10360 J. Org. Chem., Vol. 70, No. 25, 2005

OSW Saponins with Potent Antitumor Activities
FIGURE 12. Synthesis of 23-oxa-OSW-1 40.
FIGURE 13. Synthesis of OSW saponin analogues with modified side chains.
yield, while its 20R isomer was also isolated in 10% yield;
although a previous small-scale reaction (∼50 mg) af-
forded the 20S isomer 12a in 81% yield, without detection
of the 20R isomer 12b (Figure 4, entry 7). The oxidation
step with TPAP/NMO converted the 16R-OH into 16-
ketone in >90% yields, which did not affect the stereo-
chemistry of the 21-methyl group (i.e., 9a/b f 25/46, 92%;
12a f 49, 90%; 45 f 52, 92%). To obtain an analogue in
absence of the 21-methyl group (i.e., 74), aldol condensa-
tion of 6 with dodecyl acetate was carried out, after
oxidation, to lead to ketone 51 (40%). In addition, aldol
condensation of 6 with isobutyl thiopropionate was also
performed to give thioester 45 (64%), which would be
converted into the 23-S-analogue of OSW-1 (i.e., 75).
By transformations similar to those already described
in the synthesis of the 23-O-analogue of OSW-1 40
(Figure 12), that is, reduction with NaBH4/CeCl3 (25 f
27, 46-52 f 53-59), glycosylation with disaccharide
imidate 33 (27 and 53-59 f 60-67), and removal of silyl
protection (60-67 f 68-75), the desired analogues 68-
J. Org. Chem, Vol. 70, No. 25, 2005 10361

Shi et al.
FIGURE 14. Synthesis of 23-N-analogues of OSW saponins.
FIGURE 15. CM approach to the modification of the side chain of OSW saponin analogues.
75 were obtained conveniently (Figure 13). Among these
transformations, it is worth noting that reduction of the
C16-carbonyl group on C22-thioester 52 led to a consid-
erable amount of the lactonization product 26 even upon
careful quenching at low temperature. For reduction of
ketone 51, which lacks the 21-methyl group as compared
to the other substrates, the desired 16â-ol 58 was
obtained in only 59% yield, while the corresponding 16R-
ol 44 was isolated in 21% yield.
Utilizing the lactone byproduct 26, we also prepared
the 23-N-analogues 80 and 81 of OSW saponins (Figure
14). A recently developed aminolysis protocol was suc-
cessfully applied;38 thus, treatment of lactone 26 with
i-BuNH2 or (MeO)MeNH in the presence of DIBAL-H at
0 °C provided isobutyl amide 76 and Weinreb amide 77
in excellent yields. Under similar conditions, ethyl ester
27 could also be converted into amides 76 and 77 in
excellent yields.
clearly that the 16-hydroxyl configuration has a dramatic
impact, steric in origin, on the reactivity of the C22-
carbonyl function.
16â,17R-Diols 76 and 77 were then subjected to gly-
cosylation with disaccharide imidate 33 to provide gly-
cosides 78 and 79. Final removal of the silyl groups
afforded the desired 23-N-analogues 80 and 81.
The above synthetic approach to OSW saponin ana-
logues is very convenient. However, preparation of each
analogue with a different side chain requires starting
from the aldol condensation of the 16R-hydroxy-5-an-
drosten-17-one 6 with different esters; the subsequent
four steps of transformation are repetitive. It would be
ideal to modify the side chain at the final step. Such a
task could be realized by cross metathesis (CM) reaction
on a multifunctional molecule such as OSW-1.39 Thus,
we tested the CM reaction with 22-allyl ester 70 (Figure
15). Gratifyingly, treatment of allyl ester 70 with 9-decen-
1-yl benzoate 8240 (2.7 equiv) in the presence of the
Grubbs(I) catalyst (20 mol %) in refluxing CH2Cl2 pro-
vided the corresponding coupling product 83 in 22% yield.
Recalling the previous difficulty encountered in trans-
ferring 16R,17R-dihydroxyl-22-ethyl ester 8a into the
corresponding Weinreb amide 14 (Figure 5), we reexam-
ined this transformation under the present aminolysis
conditions. In contrast to 16â-22-ethyl ester 27, 16R-22-
ethyl ester 8a did not react at all. This result showed
(39) For a recent review on cross metathesis, see Connon, S. J.;
Blechert, S. Angew. Chem., Int. Ed. 2003, 42, 1900.
(40) Blackwell, H. E.; O’Leary, D. J.; Chatterjee, A. K.; Washen-
felder, R. A.; Bussmann, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 2000,
122, 58.
(38) Huang, P.; Zheng, X.; Deng, X. Tetrahedron Lett. 2001, 42, 9039.
10362 J. Org. Chem., Vol. 70, No. 25, 2005

OSW Saponins with Potent Antitumor Activities
The three cell lines tested exhibited distinct sensitivity
to OSW-1, with Jurkat T cells being most sensitive and
MCF-7 least sensitive (Table 1). Moreover, the three cell
lines have different IC50 profiles for the various side-
chain-modified OSW-1 analogues. The isosteres of OSW-1
with its 23-CH2 group replaced by S or NH group
(compounds 75 and 80) showed similar antiproliferative
potency toward HeLa and Jurkat T cells. However, the
same analogues suffered from an over 20-fold decrease
in potency in MCF-7 cells. For the C23 oxygen isostere
(40), it is slightly more potent in Jurkat T cells but is
over 10-fold less potent in either HeLa or MCF-7 cells. A
variety of the C22-ester changes, that is, from ethyl (in
68), allyl (in 70), heptyl (in 71), dodecyl (in 72), to the
9-decen-1-yl benzoate (in 83), did not affect dramatically
their antitumor activities, except for 68 and 71, toward
MCF-7 cells with a significant decrease in activity. A
longer C-17 side chain, that is, octadecyl residue (in 73),
abolished the cellular activity; and branching at the 23
position (in 81) significantly lowered the potency for
Jurkat and MCF-7 cell lines without much change in its
activity for HeLa cells. The 21-methyl group has a
significant yet intriguing impact on the cellular activities
of the compounds. The pair of 20S and 20R isomers 68
and 69 showed opposite selectivity for the inhibition of
Jurkat T in comparison to HeLa and MCF-7 cells.
Whereas the 20S isomer 68 is more potent than its
epimeric counterpart 69 in Jurkat T cells, it is signifi-
cantly less active than 69 in both HeLa and MCF-7 cells.
The importance of the 21-methyl group was underscored
by the significant reduction in potency of 74 in compari-
son with its congener 72 against all three cell lines. The
activity of the dimer 84 was significantly lower than that
of the corresponding monomer 70 in Jurkat and MCF-7
cells but was comparable to 70 in HeLa cells.
FIGURE 16. Compounds 46 and 85 for X-ray diffraction
analysis.
This yield was increased to 45% when Grubbs(II) catalyst
(6 mol %) was used with the amount of 9-decen-1-yl
benzoate 82 was lowered to 1.1 equiv. When the amount
of 9-decen-1-yl benzoate 82 was increased to 20 equiv,41
the yield of 83 was increased to 75% with Grubbs(II)
catalyst (6 mol %). In the absence of the external olefin
reagent, refluxing of 70 in CH2Cl2 in the presence of the
Grubbs(II) catalyst (19 mol %) provided the dimeric
compound 84 in 49% yield.
Confirmation of the Stereochemistry in the Ste-
roidal Aglycon Synthesis. The ready formation of the
16,22-γ-lactone 26 (Figure 10) after inversion of the
configuration of 16R-OH (of 25) implied the â orientation
of the C17 side chain, which was installed by the previous
aldol condensation. In addition, NOE interactions be-
tween the R-oriented 16-H and the 21-methyl protons and
between the â-oriented 20-H and the 18-methyl protons
were observed on this conformation-fixed lactone (Figure
10), confirming the S configuration at C-20 generated by
the same aldol reaction.
The previously assigned stereochemistry on the aldol
adducts was confirmed unambiguously by X-ray diffrac-
tion analysis of the 16-ketone derivatives 4615 and 85
(Figure 16).42 The 20R ketone 46 was obtained from the
minor aldol product 9b by TPAP/NMO oxidation (Figure
13). The 20S ketone 85 was readily synthesized from 16-
bromo-5-androsten-17-one 2 via blocking of the 3-OH
with PMB group followed by a similar transformation as
described for 4 f 6 f 11 f 37. Interestingly, it is
revealed that the C17 side chains on the 20R and 20S
steroids (e.g., 46 and 85) adopt dramatically different
trajectories in crystals. This might help to explain the
good stereo differentiation in the present aldol condensa-
tion and previous Reformatsky addition with steroidal
17-ketones.
Antitumor Activites of the OSW Saponin Ana-
logues with Modified Side Chains. The in vitro
activities of the synthetic OSW-1 and its side-chain-
modified analogues (40, 68-75, 80, 81, 83, and 84)
against the proliferation of several human cancer cell
lines including HeLa, Jurkat T cells, and human MCF-7
breast cancer cell line were determined by following the
incorporation of [3H]thymidine.43 The results are sum-
marized in Table 1.
Summary
OSW saponins, featuring a 16â,17R-dihydroxycholest-
22-one aglycon and an acylated â-D-xylopyranosyl-(1f3)-
R-L-arabinopyranosyl residue attached to the 16-hydroxyl
group (Figure 1), represent a new structural class of
natural products with extremely potent antitumor activi-
ties and a new type of mechanism of action. We found
that aldol condensation of the readily available 16R-
hydroxy-5-androsten-17-ones (Figure 3) and propionates
provided the desired 20(S)-16R,17R-dihydroxy steroidal
structure (Figures 4 and 13) in a stereocontrolled manner
in accordance with the proposed mechanism (Figure 2).
The X-ray diffraction analysis of a pair of the 20R-16-
ketone derivatives 46 and 20S- 85 confirmed unambigu-
ously the stereochemistry in the present synthesis and
revealed clearly a dramatic conformational difference
adopted by the steroidal 20S and 20R isomers.
Elaboration of the aldol adducts toward OSW-1 has
been extensively explored. Unexpectedly, the steroidal
C22 carbonyl or hydroxyl function in the presence of the
16R,17R-dihydroxy groups was found to react sluggishly;
for example, aminolysis of the 22-esters (Figure 6),
alkylation (Figure 7) and reduction (Figure 9) of 22-
Weinreb amide 14, alkylation of 22-ester 8a (Figure 8),
and umpolung alkylation of the 22-dithiane 24 (Figure
9). In sharp contrast, after inversion of the 16R-hydroxyl
configuration, the corresponding steroidal C22-carbonyl
(41) Chatterjee, A. K.; Choi, T. L.; Sanders, D. P.; Grubbs, R. H. J.
Am. Chem. Soc. 2003, 125, 11360.
(42) For the X-ray diffraction analysis data, see Supporting Informa-
tion.
(43) Zhang, Y.; Griffith, E. C.; Sage, J.; Jacks, T.; Liu, J. O. Proc.
Natl. Acad. Sci. U.S.A. 2000, 97, 6427.
J. Org. Chem, Vol. 70, No. 25, 2005 10363

Shi et al.
TABLE 1. Antitumor Activities of the Synthetic OSW-1 and Its Side Chain Modified Analogues
10364 J. Org. Chem., Vol. 70, No. 25, 2005

OSW Saponins with Potent Antitumor Activities
ESIMS m/z 765.5 (M + Na+), HRMS (ESI) m/z 765.5226 (M +
or hydroxyl functions were no longer resistant to reaction;
for example, selective acylation on the 22-OH in 16â,-
17R,22-triol 30 (Figure 11) or alkylation (Figure 10) and
aminolysis (Figure 14) of 22-ester 27 and 22,16-lactone
26.
Na+), calcd for C48H74O4SiNa 765.5249.
Compound 21: [R]D24 ) -56.7 (c 1.3, CHCl3); 1H NMR (400
MHz, CDCl3) δ 7.69-7.34 (m, 10 H), 5.11 (m, 1 H), 4.06 (m, 1
H), 3.53 (m, 1 H), 1.06 (s, 9 H), 0.98 (s, 3 H), 0.89-0.87 (8 H),
0.70 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 141.3, 135.8, 134.9,
129.5, 127.5, 121.0, 81.9, 77.1, 73.3, 49.8, 48.6, 47.1, 42.5, 37.2,
36.6, 33.2, 32.7, 32.0, 31.9, 31.8, 31.2, 28.9, 27.1, 22.8, 22.7,
20.2, 19.5, 19.2, 15.4; ESIMS m/z 637.4 (M + Na+), 1251.8 (2M
+ Na+).
By the new synthetic route, the synthesis of OSW-1
was finally achieved in a linear sequence of nine steps
and 14% overall yield from the aldol adduct 9a (Figures
10 and 11) without much optimization. We found that
the present chemistry was extremely convenient for the
synthesis of the OSW saponin analogues with a C22-ester
side chain. Remarkably, a 23-oxa analogue of OSW-1, 40,
was prepared starting from the industrial dehydroisoan-
drosterone 1 in eight linear steps and in 26% overall yield
(Figure 12). And this 23-oxa analogue was found to be
as active as the parent OSW-1. Thus, a new stage was
set for further synthesis to decipher SAR of OSW sa-
ponins.
With the ready chemistry in hand, analogues with a
variety of modified side chains were easily prepared, via
aldol condensation with propionates of varying length,
with thiopropionate and acetate (for preparation of 68-
75; Figure 13), or via aminolysis of the 16,22-lactone 26
(for preparation of the 23-N-analogues; Figure 14). CM
reaction was also proven feasible for modification at the
final stage from C22-allyl ester 70 (Figure 15). Examina-
tion of these new analogues revealed a valuable SAR for
the side chain of OSW saponins (Table 1). The new
synthetic routes to OSW-1 and its side-chain analogues
also pave the way to synthesis of new probes for mecha-
nistic studies of OSW-1 and of selected active analogues
in gram quantities for animal studies.
Compound 22: [R]D24 ) -57.4 (c 1.5, CHCl3); 1H NMR (400
MHz, CDCl3) δ 7.69-7.34 (m, 10 H), 5.11 (m, 1 H), 4.32 (m, 1
H), 3.56-3.48 (m, 1 H), 1.05 (s, 9 H), 0.99 (s, 3 H), 0.91 (s, 3
H), 0.89 (s, 3 H), 0.86 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ
141.7, 136.2, 135.2, 129.8, 127.8, 121.1, 85.5, 81.8, 73.5, 50.2,
48.9, 47.6, 42.8, 37.5, 36.9, 34.1, 33.8, 33.3, 32.8, 32.2, 31.9,
29.8, 28.5, 27.4, 23.1, 23.0, 20.7, 19.8, 19.5, 15.1; ESIMS m/z
637.4 (M + Na+), HRMS (ESI) m/z 637.4031 (M + Na+), calcd
for C40H58O3SiNa 637.4047.
16,22-γ-Lactone 26. A suspension of 2515 (318 mg, 0.61
mmol), CeCl3‚7H2O (320 mg, 0.86 mmol), and NaBH4 (160 mg,
4.21 mmol) in dry THF was stirred at 0 °C for 1 h and then
quenched with methanol. After the mixture was stirred for
about 0.5 h, water was added. The resulting mixture was
diluted with CH2Cl2. The organic layer was washed with 5%
HCl and brine, respectively, and then dried over Na2SO4 and
filtered. The filtrate was concentrated in vacuo to give a
residue, which was purified by flash column chromatography
(petroleum ether/EtOAc/CH2Cl2 9:1:2) to afford 26 (267 mg,
26
1
92%) as a white solid. [R]D ) -85.2 (c 0.3, CHCl3); H NMR
(400 MHz, CDCl3) δ 5.26 (m, 1 H), 4.43 (dd, J ) 4.7 and 3.2
Hz, 1 H), 3.46-3.39 (m, 1 H), 2.67 (q, J ) 7.7 Hz, 1 H), 1.29
(d, J ) 7.7 Hz, 3 H), 1.03 (s, 3 H), 0.89 (s, 9 H), 0.81 (s, 3 H),
0.06 (s, 6 H); ESIMS m/z 492.4 (M + Na+), 971.6 (2M + Na+).
Anal. Calcd for C28H46O4Si: C, 70.84; H, 9.77. Found: C, 71.03;
H, 9.78.
16â,17R,22-Triol 30. To a solution of lactone 26 (147 mg,
0.31 mmol) in THF (5 mL) was added dropwise a solution of
isoamyllithium in Et2O (1.35 M, 1.83 mL, 2.48 mmol) during
0.5 h at room temperature under argon. The reaction mixture
was quenched with saturated aqueous NH4Cl. The product was
extracted with CH2Cl2. The combined organic layer was
washed with brine and dried over anhydrous Na2SO4. The
solvent was removed to afford the crude hemiketal 28, which
was used immediately without further purification and iden-
tification. Hemiketal 28 was dissolved in anhydrous ether (20
mL). The solution was cooled to 0 °C and treated with a
suspension of LiAH4 (59 mg, 1.55 mmol) in ether (2 mL). The
reaction mixture was stirred overnight at room temperature.
After completion of the reaction, excess LiAH4 was quenched
carefully with water. The product was extracted with ether.
The organic extract was washed with 5% HCl and brine,
respectively, and was then dried over Na2SO4 and filtered. The
filtrate was concentrated in vacuo to give a residue, which was
purified by silica gel flash column chromatography (petroleum
ether/EtOAc/CH2Cl2 6:1:1) to afford 30 (147 mg, 87%) as a
white solid. Compound 30 is a mixture of the epimers at C22.
Experimental Section44
Isoamyl Ketone 17 (and Byproducts 20-22). A solution
of 8a (400 mg, 0.62 mmol) in dry THF (6 mL) was cooled to
-20 °C under Ar. Isoamyllithium (8 mL, 0.78 M in Et2O) was
added dropwise with stirring over 15 min. After being stirred
at -20 °C for an additional 1.5 h, the resulting reaction
mixture was pooled into 5% HCl that has been cooled to -40
°C. The product was extracted with CH2Cl2, and the combined
organic layers were dried over Na2SO4. After evaporation of
the solvent, the residue was purified by flash column chro-
matography (petroleum ether/EtOAc 12:1) to afford 17 (121
mg, 34%), 20 (69 mg, 17%), 21 (80 mg, 19%), 22 (24 mg, 6%),
and 5 (6%) as white solids.
Compound 17: [R]D24 ) -52.5 (c 1.0, CHCl3); 1H NMR (300
MHz, CDCl3) δ 7.69-7.34 (m, 10 H), 5.10 (m, 1 H), 4.04 (br s,
1 H), 4.05-3.96 (m, 1 H), 3.54 (m, 1 H), 2.88 (q, J ) 7.1 Hz, 1
H), 2.54 (t, J ) 7.4 Hz, 2 H), 2.54 (br s, 1 H), 1.16 (d, J ) 7.1
Hz, 3 H), 1.06 (s, 9 H), 0.97 (s, 3 H), 0.9 (s, 3 H), 0.88 (s, 3 H),
0.78 (s, 3 H); 13C NMR (75 MHz, CDCl3) δ 218.4, 141.2, 135.7,
134.8, 129.4, 127.4, 120.8, 82.6, 76.9, 73.1, 79.4, 49.3, 48.2, 48.2,
42.4, 41.6, 37.0, 36.4, 35.2, 32.3, 32.1, 31.8, 31.7, 27.5, 27.0,
22.3, 20.2, 19.4, 19.1, 14.5, 12.7; ESIMS m/z 693.4 (M + Na+),
HRMS (ESI) m/z 693.4288 (M + Na+), calcd for C43H62O4SiNa
693.4310.
22-O-AZMB Ester 31 (and 16-O-AZMB Ester 32). To a
stirring solution of triol 30 (140 mg, 0.26 mmol) in anhydrous
THF (6 mL) at room temperature was added DMAP (120 mg,
0.98 mmol), followed by addition of a solution of 2-(azidom-
ethyl)benzoyl chloride37 (3.9 mL, 0.33 M) in THF. After
completion of the reaction, the reaction mixture was diluted
with CH2Cl2 and washed twice with saturated aqueous NaH-
CO3 and once with water. The organic layer was dried over
Na2SO4, filtered, and concentrated in vacuo. The crude product
was purified by flash column chromatography (petroleum
ether/EtOAc 30:1 to petroleum ether/EtOAc 15:1) to afford 31
(87 mg, 48%) and the 16-O-AZMB ester 32 (7%) as white solids.
Compound 20: 1H NMR (500 MHz, CDCl3) δ 7.67-7.35 (m,
10 H), 5.10 (m, 1 H), 4.52 (br s, 1 H), 4.39 (m, 1 H), 3.54 (m, 1
H), 2.99 (br s, 1 H), 1.06 (s, 9 H), 0.97 (s, 3 H), 0.9 (s, 3 H),
0.89-0.86 (16 H), 0.78 (s, 3 H); 13C NMR (75 MHz, CDCl3) δ
141.2, 135.7, 134.8, 129.4, 127.4, 121.0, 84.6, 79.7, 75.8, 73.2,
49.4, 48.1, 43.0, 42.5, 37.0, 33.33, 33.28, 42.25, 31.93, 31.86,
31.80, 28.6, 27.0, 22.97, 22.82, 22.66, 22.39, 19.4, 14.3, 13.0;
Compound 31: [R]D14 ) -11.1 (c 1.0, CHCl3); 1H NMR (300
MHz, CDCl3) δ 8.05 (d, J ) 8.1 Hz, 1 H), 7.58 (d, J ) 7.2 Hz,
1 H), 7.55 (t, J ) 7.2 Hz, 1 H), 7.43 (t, J ) 7.2 Hz, 1 H), 5.31
(44) For compounds not been described in this section, see Support-
ing Information.
J. Org. Chem, Vol. 70, No. 25, 2005 10365

Shi et al.
(m, 1 H), 5.16 (d, J ) 10.2 Hz, 1 H), 4.91-4.77 (m, 3 H), 4.15
(m, 1 H), 3.56-3.40 (m, 1 H), 2.46 (q, J ) 6.4 Hz, 1 H), 1.12
(d, J ) 7.1 Hz, 3 H), 1.01 (s, 3 H), 0.97 (s, 3 H), 0.89 (s, 9 H),
0.88 (d, J ) 7.2 Hz, 6 H), 0.06 (s, 6 H); 13C NMR (75 MHz,
CDCl3) δ 168.0, 141.4, 137.9, 133.1, 131.1, 129.7, 128.3, 128.1,
120.9, 86.4, 79.5, 78.9, 72.5, 53.1, 49.8, 48.5, 47.1, 42.7, 38.9,
37.3, 36.5, 35.8, 34.5, 32.7, 32.0, 31.9, 31.8, 28.5, 27.8, 25.9,
22.9, 22.3, 20.4, 19.4, 18.3, 12.8, 9.9, -4.6; ESIMS m/z 730.5
(M + Na+), HRMS (ESI) m/z 730.4596 (M + Na+), calcd for
C41H65O5N3SiNa 730.4586.
J ) 9.3 Hz, 2 H), 6.85 (d, J ) 8.7 Hz, 2 H), 5.24 (m, 1 H), 4.87
(m, 1 H), 4.76 (m, 1 H), 4.69 (m, 1 H), 4.17 (m, 1 H), 3.81 (s, 3
H), 3.06 (q, J ) 7.2 Hz, 1 H), 2.20-2.13 (m, 1 H), 1.90 (s, 3 H),
1.09 (d, J ) 7.2 Hz, 3 H), 0.07 (s, 6 H); 13C NMR (75 MHz,
CDCl3) δ 219.5, 168.7, 164.7, 163.5, 141.4, 132.0, 122.6, 121.1,
113.5, 100.0, 85.9, 72.6, 69.8, 55.4, 49.6, 48.1, 46.1, 45.9, 42.8,
39.0, 37.3, 36.5, 34.6, 32.2, 31.9, 29.7, 27.4, 25.9, 22.4, 22.1,
20.7, 19.3, 18.3, 13.9, 11.8, 6.9, 6.8, 4.9, 4.8, -4.6; ESIMS m/z
1351.8 (M + Na+), HRMS (ESI) m/z 1351.7890 (M + Na+),
calcd for C71H124O15Si4Na 1351.7910.
Compound 32: 1H NMR (300 MHz, CDCl3) δ 8.04 (d, J )
8.1 Hz, 1 H), 7.56 (d, J ) 7.2 Hz, 1 H), 7.52 (t, J ) 7.2 Hz, 1
H), 7.42 (t, J ) 7.2 Hz, 1 H), 5.64-5.59 (dd, J ) 7.8 and 9.0
Hz, 1 H), 5.32 (m, 1 H), 4.97-4.74 (AB, 2 H), 4.83 (m, 1 H),
4.23 (m, 1 H), 3.48 (m, 1 H), 1.13 (d, J ) 7.2 Hz, 3 H), 1.01 (s,
3 H), 0.94 (s, 3 H), 0.89 (s, 9 H), 0.88 (d, J ) 7.2 Hz, 6 H), 0.06
(s, 6 H); 13C NMR (75 MHz, CDCl3) δ 167.7, 141.5, 137.5, 132.7,
131.0, 129.6, 128.1, 120.9, 86.8, 80.6, 77.2, 72.5, 53.2, 49.7, 48.4,
46.6, 42.8, 38.6, 37.3, 37.1, 36.5, 34.8, 32.6, 32.4, 32.0, 31.9,
31.9, 27.9, 26.0, 22.8, 22.4, 20.5, 19.4, 18.3, 13.4, 9.0, -4.6.
OSW-1. A solution of 36 (14.1 mg, 0.011 mmol) and
Pd(MeCN)2Cl2 (cat. 1.5 mg) in acetone and water (20:1 v/v, 1
mL) was stirred at room temperature until TLC indicated the
reaction has finished. Then the solution was directly concen-
trated in vacuo to give a residue, which was purified by silica
gel column chromatography (CH2Cl2/MeOH 15:1) to give OSW-
11,6 (7.6 mg, 82%) as a white solid. [R]D16 ) -42.9 (c 0.14, CH3-
OH).
(20S)-Allyl-23-oxa-OSW-1 70. A solution of 62 (188 mg,
0.143 mmol) in dry CH2Cl2 (10 mL) was treated with HF-
pyridine (2 drops) at room temperature. After being stirred
for 0.5 h, the reaction mixture was poured into a saturated
NaHCO3 solution. The organic layer was washed with brine
and dried over Na2SO4. After evaporation of the solvent, the
residue was purified by silica gel column chromatography
(CH2Cl2/MeOH 30:1) to afford 70 (118 mg, 96%) as a white
Glycoside 34. A solution of the disaccharide imidate 336
(160 mg, 0.13 mmol), aglycon 31 (81 mg, 0.11 mmol), and 4 Å
molecular sieve in dry CH2Cl2 was stirred at room temperature
for 15 min and then cooled to -20 °C. A solution of TMSOTf
(0.05 equiv) in CH2Cl2 was slowly added to the reaction. After
being stirred for 1 h, the reaction was quenched with Et3N
and filtered. The filtrates were concentrated in vacuo to give
a residue, which was purified by silica gel column chromatog-
raphy (petroleum ether/EtOAc 20:1) to afford 34 (104 mg, 61%)
foam. [R]D ) -31.3 (c 0.59, CHCl3); 1H NMR (300 MHz,
26
CDCl3) δ 8.03 and 6.93 (AB, 4 H), 5.71-5.59 (m, 1 H), 5.32
(m, 1 H), 5.16 (d, J ) 7.8 Hz, 1 H), 5.11 (br s, 1 H), 4.93 (dd,
J ) 6.6 and 6.3 Hz, 1 H), 4.83-4.76 (m, 2 H), 4.55 (dd, J )
12.6 and 6.0 Hz, 1 H), 3.91 (s, 3 H), 2.61 (q, J ) 7.2 Hz, 1 H),
1.94 (s, 3 H), 1.05-0.90 (m, 7 H), 0.78 (s, 3 H); 13C NMR (75
MHz, CDCl3) δ 181.2, 172.2, 168.6, 166.6, 143.2, 134.8, 134.4,
124.1, 124.0, 121.3, 116.5, 103.2, 102.6, 92.2, 87.3, 76.4, 75.7,
74.4, 72.7, 72.0, 67.7, 67.4, 66.5, 64.1, 58.1, 56.0, 52.2, 50.9,
48.5, 44.9, 43.2, 39.8, 39.1, 37.4, 34.4, 34.2, 23.4, 23.2, 22.1,
15.9, 15.3; ESIMS m/z 881.5 (M + Na+), HRMS (ESI) m/z
881.3949 (M + Na+), calcd for C45H62O16Na 881.3930.
20
1
as a white foam. [R]D ) -25.5 (c 1.7, CHCl3); H NMR (300
MHz, CDCl3) δ 7.86 (d, J ) 8.1 Hz, 3 H), 7.49 (m, 3 H), 6.76
(d, J ) 8.1 Hz, 2 H), 5.31 (m, 1 H), 5.20 (m, 2 H), 4.90 (m, 2
H), 4.87 and 4.69 (AB, 2 H), 4.52 (d, J ) 3.6 Hz, 1 H), 4.24 (br
s, 1 H), 4.02 (m, 1 H), 3.84 (s, 3 H), 1.68 (s, 3 H), 1.07 (d, J )
6.9 Hz, 3 H), 0.07 (s, 6 H); 13C NMR (75 MHz, CDCl3) δ 168.0,
163.9, 162.5, 140.8, 136.8, 131.6, 131.2, 130.3, 129.2, 128.6,
127.1, 122.1, 120.5, 112.7, 100.5, 86.4, 76.7, 76.1, 72.0, 54.8,
52.4, 49.3, 48.3, 47.1, 42.2, 38.0, 36.8, 35.9, 35.0, 32.1, 31.5,
31.4, 31.2, 30.0, 29.2, 27.4, 25.4, 24.2, 22.3, 20.1, 20.0, 18.7,
17.8, 17.7, 12.6, 10.5, 6.4, 6.38, 6.3, 4.6, 4.5, 4.4, 4.4, 4.3, 4.2,
-5.1; ESIMS m/z 1513.1 (M + Na+), HRMS (ESI) m/z
1512.8509 (M + Na+), calcd for C79H131O16N3Si4Na 1512.8499.
22-Amide 76. A solution of DIBAL-H (1 M in toluene, 4.9
mL, 4.9 mmol) was added to a cool (0∼5 °C) solution of
isobutylamine (0.5 mL, 0.5 mmol) in THF (2 mL) under argon.
The mixture was allowed to warm and was stirred at room
temperature for 2 h. The concentration of the prepared DIBAL-
H/i-BuNH2 complex was about 0.72 mol/L.
22-Alcohol 35. To a solution of 34 (30 mg, 0.02 mmol) in
THF (1 mL) was added water (5 equiv), followed by tribu-
tylphosphine (15 µL, 0.06 mmol) at room temperature. After
being stirred for 30 min, the reaction mixture was diluted with
CH2Cl2 and washed once with saturated aqueous NaHCO3 and
twice with water. The organic layer was dried over Na2SO4,
filtered, and concentrated in vacuo. The crude product was
purified by silica gel column chromatography (petroleum ether/
To a solution of 26 (30 mg, 0.063 mmol) in THF (2 mL) were
added, under Ar at room temperature, the DIBAL-H/i-BuNH2
complexes (0.44 mL, 0.72 mol/L). After being stirred at room
temperature for 2 h, the reaction was cooled to 0 °C and then
quenched with H2O (0.1 mL) and a 1 N aqueous solution of
KHSO4 (5 mL). The resulting mixture was extracted with CH2-
Cl2. The combined organic layers were washed with brine,
dried over Na2SO4, and concentrated. The residue was purified
by flash chromatography (petroleum ether/EtOAc 5:1) to afford
76 (33 mg, 95%) as a white solid. [R]D20 ) -39.2 (c 0.5, CHCl3);
1H NMR (300 MHz, CDCl3) δ 5.77 (br s, 1 H), 5.29 (m, 1 H),
4.21 (s, 1 H), 3.92 (m, 1 H), 3.50-3.43 (m, 1 H), 3.11 (m, 2 H),
2.86 (q, J ) 7.2 Hz, 1 H), 2.66 (m, 1 H), 1.24 (d, J ) 7.2 Hz, 3
H), 1.13 (s, 3 H), 0.98 (s, 3 H), 0.91 (s, 3 H), 0.88 (d, 9 H); 13C
NMR (75 MHz, CDCl3) δ 178.4, 141.5, 120.8, 85.1, 81.8, 72.5,
49.6, 48.4, 46.7, 46.3, 42.7, 41.8, 37.3, 36.5, 35.8, 32.6, 32.0,
31.9, 31.8, 28.5, 25.9, 20.4, 20.1, 19.4, 18.2, 13.4, -4.6; ESIMS
m/z 570.4 (M + Na+), HRMS (ESI) m/z 570.3963 (M + Na+),
calcd for C32H57NO4SiNa 570.3949.
Protected 23-Aza-OSW-1 78. A procedure similar to that
described for the preparation of 34 was employed. Thus
treatment of 76 (33 mg, 0.06 mmol) and disaccharide imidate
33 (70 mg, 0.072 mmol) in the presence of TMSOTf (30 µL,
0.1 M solution in CH2Cl2) provided 78 (52 mg, 65%) as a white
foam. [R]D20 ) -24.3 (c 1.6, CHCl3); 1H NMR (300 MHz, CDCl3)
δ 8.03 and 6.93 (AB, 4 H), 7.20 (m, 1 H), 5.62 (s, 1 H), 5.30 (m,
1 H), 4.89 (s, 1 H), 4.82 (m, 2 H), 4.45 (2 H), 3.89 (s, 3 H), 3.49
(m, 1 H), 3.12 (q, J ) 7.4 Hz, 1 H), 1.99 (s, 3 H), 1.32 (d, J )
21
EtOAc 15:1) to afford 35 (22 mg, 82%) as a white solid. [R]D
) -36.8 (c 1.4, CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.00 (d,
J ) 9.6 Hz, 2 H), 6.88 (d, J ) 8.7 Hz, 2 H), 5.30 (m, 1 H), 4.94
(dd, J ) 2.4 and 5.4 Hz, 1 H), 4.87 (m, 2 H), 4.49 (d, J ) 3.0
Hz, 1 H), 4.26 (m, 1 H), 4.22 (m, 1 H), 3.86 (s, 3 H), 2.61 (m,
1 H), 1.95 (s, 3 H), 0.07 (s, 6 H); 13C NMR (75 MHz, CDCl3):
δ 170.0, 164.7, 163.3, 141.5, 131.9, 122.6, 121.1, 113.4, 113.1,
100.5, 90.4, 87.1, 82.4, 77.2, 75.6, 72.9, 72.6, 70.7, 70.1, 62.9,
56.6, 56.3, 55.4, 49.6, 48.4, 48.1, 47.0, 44.6, 43.4, 42.8, 41.0,
37.5, 37.3, 36.5, 35.7, 35.0, 34.7, 33.3, 32.2, 32.1, 31.9, 31.5,
30.1, 29.7, 27.8, 25.9, 25.0, 24.4, 22.9, 22.2, 21.4, 20.9, 20.6,
19.2, 18.2, 17.1, 13.3, 13.1, 6.9, 6.8, 4.9, 4.8, -4.6; ESIMS m/z
1354.5 (M + Na+), HRMS (ESI) m/z 1353.8064 (M + Na+),
calcd for C71H126O15Si4Na 1353.8066.
22-Ketone 36. To a solution of 35 (21 mg, 0.016 mmol) and
3 Å molecular sieve (20 mg) in CH2Cl2 was added pyridinium
dichromate (12 mg, 0.032 mmol). After being stirred for 1 h
at room temperature, the reaction mixture was filtered. The
filtrates were evaporated in vacuo. The crude product was
purified by silica gel column chromatography (petroleum ether/
20
EtOAc 15:1) to afford 36 (20.3 mg, 97%) as a white solid. [R]D
) -43.5 (c 0.7, CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.00 (d,
10366 J. Org. Chem., Vol. 70, No. 25, 2005

OSW Saponins with Potent Antitumor Activities
7.4 Hz, 3 H), 0.06 (s, 6 H); 13C NMR (75 MHz, CDCl3) δ 180.1,
169.1, 166.7, 163.4, 141.3, 132.0, 122.0, 121.1, 113.6, 100.5,
98.1, 91.2, 85.5, 76.1, 73.9, 72.5, 71.9, 70.6, 68.4, 65.3, 63.2,
59.7, 55.5, 49.6, 48.2, 46.1, 45.7, 42.9, 40.4, 37.2, 36.5, 35.0,
32.3, 32.1, 31.9, 28.2, 25.9, 20.7, 20.6, 20.2, 20.1, 19.2, 18.2,
14.5, 14.4, 6.9, 6.7, 5.1, 5.0, 4.7, -4.6; MALDI-MS m/z 1352.7
(M + Na+), HRMS (MALDI) m/z 1352.7905 (M + Na+), calcd
for C70H123NaNO15Si4 1352.7862.
69.5, 64.6, 64.5, 54.9, 49.0, 47.8, 45.3, 40.0, 36.7, 35.9, 31.7,
31.6, 31.3, 31.2, 31.1, 29.2, 28.8, 28.7, 28.6, 28.3, 28.2, 25.5,
20.2, 18.9, 12.8, 12.1; ESIMS m/z 1113.65 (M + Na+), HRMS
(MALDI) m/z 1113.5371 (M + Na+), calcd for C60H82O18Na
1113.5393.
Dimer 84. Allyl ester 70 (25 mg, 0.029 mmol) was added
via syringe to a stirring solution of Grubbs second-generation
catalyst (4.7 mg, 0.0055 mmol) in CH2Cl2 (5 mL). The flask
was fitted with a condenser and refluxed under nitrogen for
16 h. The reaction mixture was then concentrated and purified
directly by silica gel column chromatography (CH2Cl2/MeOH
30:1) to afford 84 as a white solid (12 mg, 49%). [R]D21 ) -10.1
(c 0.6, CHCl3); 1H NMR (500 MHz, C6D5N) δ 8.42 (d, J ) 10.0
Hz, 1 H), 7.18 (d, J ) 10.0 Hz, 1 H), 6.09 (m, 1 H), 5.77 (m, 2
H), 5.45 (br s, 1 H), 5.34 (d, J ) 5.0 Hz, 1 H), 4.70 (d, J ) 5.0
Hz, 1 H), 4.58-4.28 (m, 10 H), 3.87 (m, 6 H), 3.08 (m, 1 H),
2.77 (br s, 1 H), 2.68-2.67 (d, J ) 5.0 Hz, 1 H), 2.10 (m, 6 H),
1.13 (s, 3 H); 13C NMR (125 MHz, C6D5N) δ 178.1, 169.8, 165.7,
164.0, 142.0, 132.5, 129.1, 121.2, 114.2, 103.2, 85.1, 75.9, 75.2,
71.6, 71.4, 70.8, 55.7, 50.3, 49.0, 46.7, 43.6, 41.4, 37.9, 36.9,
32.7, 32.3, 32.2, 30.8, 30.1, 30.0, 29.7, 29.3, 23.0, 21.0, 21.0,
19.7, 17.8, 14.3, 13.6, 13.4; ESIMS m/z 1711.7 (M + Na+),
HRMS (ESI) m/z 1711.7637 (M + Na+), calcd for C88H120O32-
Na 1711.7654.
23-Aza-OSW-1 analogue 80. A procedure similar to that
described for the preparation of OSW-1 was employed. Thus
treatment of 78 (40 mg, 0.030 mmol) with Pd(MeCN)2Cl2 (1.8
mg) provided 80 (19.6 mg, 75%) as a white foam. [R]D20 ) -45.3
(c 0.9, CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.07 and 6.99 (AB,
4 H), 5.64 (m, 1 H), 5.32 (m, 1 H), 5.27 (s, 1 H), 4.90 (br s, 1
H), 4.89 (m, 1 H), 4.71 (m, 1 H), 4.39 (br s, 1 H), 4.32 (m, 1 H),
4.28 (m, 1 H), 3.96 (br s, 1 H), 3.88 (s, 3 H), 2.58 (q, J ) 7.4
Hz, 1 H), 2.02 (s, 3 H), 1.19 (d, J ) 7.4 Hz, 3 H), 1.00 (s, 3 H),
0.84 (s, 3 H), 0.79 (d, J ) 6.6 Hz, 6 H); 13C NMR (75 MHz,
CDCl3) δ 179.4, 169.6, 166.0, 164.3, 140.5, 132.2, 121.6, 121.0,
114.2, 99.5, 99.4, 90.4, 85.3, 76.1, 72.6, 72.4, 71.7, 70.3, 69.1,
63.7, 63.0, 59.6, 55.6, 49.5, 48.0, 46.2, 45.7, 42.3, 40.6, 37.1,
36.4, 34.7, 32.2, 31.8, 31.6, 28.2, 20.8, 20.6, 20.0, 19.9, 19.4,
14.5, 13.5; MALDI-MS m/z 896.5 (M + Na+), HRMS (MALDI)
m/z 896.4446 (M + Na+), calcd for C46H67O15NaN 896.4403.
Compound 83. Allyl ester 70 (21 mg, 0.025 mol) and
9-decen-1-yl benzoate 82 (125 mg, 0.48 mmol) were added via
syringe to a stirring solution of Grubbs second-generation
catalyst (1.5 mg, 0.0018 mmol) in CH2Cl2 (2 mL). The flask
was fitted with a condenser and refluxed under nitrogen for
16 h. The reaction mixture was then concentrated and purified
directly by silica gel column chromatography (CH2Cl2/MeOH
30:1) to afford 83 (20 mg, 75%) as a white solid. [R]D26 ) -21.7
Acknowledgment. This work is supported by the
NationalNaturalScienceFoundationofChina(20372070,
20321202, and 29925203), the Chinese Academy of
Sciences (KGCX2-SW-209), and the Committee of Sci-
ence and Technology of Shanghai (04DZ14901 and
04DZ05603).
1
(c 0.76, CHCl3); H NMR (500 MHz, CDCl3) δ 8.03 (m, 4 H),
Supporting Information Available: Experimental pro-
cedures for synthesis and cell proliferation assay, spectroscopic
data for other new compounds, reproductions of 1H and 13C
NMR spectra for selected compounds (in total 159 spectra),
and X-ray diffraction data for compounds 46 and 85. This
material is available free of charge via the Internet at
http://pubs.acs.org.
7.55 (m, 1 H), 7.44 (m, 2 H), 6.93 (d, J ) 5.0 Hz, 2 H), 5.64 (m,
1 H), 5.36-5.29 (m, 2 H), 4.94 (br s, 1 H), 4.84 (m, 2 H), 4.57
(m, 1 H), 4.31 (t, J ) 10.0 Hz, 2 H), 4.23 (br s, 1 H), 4.16 (m,
1 H), 4.02 (m, 1 H), 3.86 (br s, 1 H), 3.84-3.78 (m, 9 H), 3.67
(m, 1 H), 3.51-3.37 (m, 4 H), 1.96 (s, 3 H),0.78 (s, 3 H); 13C
NMR (125 MHz, CDCl3) δ 178.1, 169.1, 166.2, 165.4, 163.4,
140.1, 136.5, 132.3, 131.6, 130.0, 129.0, 127.8, 122.8, 121.0,
120.9, 113.4, 99.9, 99.5, 89.1, 84.2, 76.7, 76.5, 76.2, 72.5, 71.3,
JO051536B
J. Org. Chem, Vol. 70, No. 25, 2005 10367