Solid and solution phase synthesis and biological evaluation of combinatorial sarcodictyin libraries

Article abstract of DOI:10.1021/ja9823870

Isolated from certain species of soft corals, the sarcodictyins, eleutherobin, and eleuthosides have become important synthetic targets due the their novel molecular architectures, important biological activities, and potential in medicine. Of particular interest is their Taxol-like mechanism of action involving disturbance of the tubulin-microtubule interplay resulting in tumor cell death. Their scarcity and biological profile prompted us to initiate a program directed at exploring their chemical synthesis and chemical biology. Herein we report (a) the first total synthesis of sarcodictyins A (7) and B (8) by a combination of solution and solid-phase methods through the attachment of the common precursors 18 or 20 on solid support, thus generating conjugates 23 and 24, followed by standard chemical manipulations; (b) the construction of a combinatorial library of sarcodictyins by solution and solid-phase chemistry modifying the C-8 ester, C-15 ester, and C-4 ketal functionalities, and, therefore, producing analogues of the general structures 33, 37, and 40; (c) the tubulin polymerization properties of all members of the library; and (d) the cytotoxic actions of a selected number of these compounds against a number of tumor cells including Taxol-resistant lines. Several of the synthesized analogues were identified to be of equal or superior biological activities (e.g. 60, 61, 63, 66-70, 73, 76, 85, 92) as compared to the natural products, setting the stage for further developments in the field of cancer chemotherapy.

Full text of DOI:10.1021/ja9823870

10814
J. Am. Chem. Soc. 1998, 120, 10814-10826
Solid and Solution Phase Synthesis and Biological Evaluation of
Combinatorial Sarcodictyin Libraries
K. C. Nicolaou,* N. Winssinger, D. Vourloumis, T. Ohshima, S. Kim, J. Pfefferkorn,
J.-Y. Xu, and T. Li
Contribution from the Department of Chemistry and The Skaggs Institute for Chemical Biology,
The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, and
Department of Chemistry and Biochemistry, UniVersity of California, San Diego, 9500 Gilman DriVe,
La Jolla, California 92093
ReceiVed July 7, 1998
Abstract: Isolated from certain species of soft corals, the sarcodictyins, eleutherobin, and eleuthosides have
become important synthetic targets due the their novel molecular architectures, important biological activities,
and potential in medicine. Of particular interest is their Taxol-like mechanism of action involving disturbance
of the tubulin-microtubule interplay resulting in tumor cell death. Their scarcity and biological profile prompted
us to initiate a program directed at exploring their chemical synthesis and chemical biology. Herein we report
(a) the first total synthesis of sarcodictyins A (7) and B (8) by a combination of solution and solid-phase
methods through the attachment of the common precursors 18 or 20 on solid support, thus generating conjugates
23 and 24, followed by standard chemical manipulations; (b) the construction of a combinatorial library of
sarcodictyins by solution and solid-phase chemistry modifying the C-8 ester, C-15 ester, and C-4 ketal
functionalities, and, therefore, producing analogues of the general structures 33, 37, and 40; (c) the tubulin
polymerization properties of all members of the library; and (d) the cytotoxic actions of a selected number of
these compounds against a number of tumor cells including Taxol-resistant lines. Several of the synthesized
analogues were identified to be of equal or superior biological activities (e.g. 60, 61, 63, 66-70, 73, 76, 85,
92) as compared to the natural products, setting the stage for further developments in the field of cancer
chemotherapy.
Introduction
Sarcodictyins A (7) and B (8) (Figure 1) were discovered in
the Mediterranean stoloniferan coral Sarcodictyon roseum by
Pietra et al. and originally reported in 1987.1 The sarcodictyin
family was enriched in 1988 with the disclosure of the structures
of sarcodictyins C-F from the same group.2 Their potent
antitumor activity and Taxol-like mode of action (i.e. tubulin
polymerization and microtubule stabilization)3 were recognized
in 1997 by an Upjohn-Pharmacia group.4 These substances are
related, both structurally and with regard to their biological
action, to eleutherobin (4)5 and to eleuthosides A (5) and B
(6)6 (Figure 1). Furthermore, all four marine-derived natural
(1) D’Ambrosio, M.; Guerriero, A.; Pietra, F. HelV. Chim. Acta 1987,
70, 2019-2027.
(2) D’Ambrosio, M.; Guerriero, A.; Pietra, F. HelV. Chim. Acta 1988,
71, 964-976.
(3) Schiff, P. B.; Fant, J.; Horwitz, S. B. Nature (London) 1979, 277,
665-667.
(4) Ciomei, M.; Albanese, C.; Pastori, W.; Grandi, M.; Pietra, F.;
D’Ambrosio, M.; Guerriero, A.; Battistini, C. Proc. Am. Assoc. Cancer Res.
1997, 38, 5, Abstract 30.
(5) (a) Fenical, W.-H.; Hensen, P. R.; Lindel, T. US 5,473,057; Chem.
Abstr. 1996, 124, 194297z. (b) Lindel, T.; Jensen, P. R.; Fenical, W.; Long,
B. H.; Casazza, A. M.; Carboni, J.; Fairchild, C. R. J. Am. Chem. Soc.
1997, 119, 8744-8745. (c) Long, B. H.; Carboni, J. M.; Wasserman, A. J.;
Cornell, L. A.; Casazza, A. M.; Jensen, P. R.; Lindel, T.; Fenical, W.;
Fairchild, C. R. Cancer Res. 1998, 58, 1111-1115. (d) Ter Haar, E. Expert
Opin. Ther. Pat. 1998, 8, 571-586.
(6) (a) Ketzinel, S.; Rudi, A.; Schleyer, M.; Benayahu, Y.; Kashman,
Y. J. Nat. Prod. 1996, 59, 873-875. (b) The general name “eleuthosides”
has been used for other marine natural products: Shibuya, H.; Fukushima,
T.; Ohashi, K.; Nakamura, A.; Riswan, S.; Kitagawa, I. Chem. Pharm. Bull.
1997, 45, 1130-34.
Figure 1. Molecular structures of Taxol (1), epothilones A (2) and B
(3), eleutherobin (4), eleuthosides A (5) and B (6), and sarcodictyins
A (7) and B (8) (Ac ) acetyl, Bz ) benzoyl).
products (4-8) share the same mechanism of action with the
soil-derived (myxobacteria) epothilones A (2) and B (3)7-10
(Figure 1) and the forest-residing Taxol (1)11 (Figure 1). The
latter compound 1 is currently enjoying a billion-dollar drug
status as an anticancer agent. Total syntheses of eleutherobin
(4),12-14 eleuthosides A (5) and B (6),13 and sarcodictyins A
(7) and B (8)15,16 have recently been reported. Furthermore, the
10.1021/ja9823870 CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/09/1998

Combinatorial Sarcodictyin Libraries
J. Am. Chem. Soc., Vol. 120, No. 42, 1998 10815
syntheses of a number of sarcodictyin analogues have also been
accomplished in solution and recently disclosed from these
laboratories.17 In this article we describe the development of
solid-phase chemistry that allowed the generation of a combi-
natorial sarcodictyin library and its biological evaluation leading
to the discovery of analogues possessing higher antitumor
potencies than those of the natural products. The gained
knowledge provides important information regarding the struc-
ture-activity relationships within the sarcodictyin-eleutherobin
molecular framework and sets the stage for further advances in
the field.
Molecular Diversity Design. Solid Phase Strategy. Inspec-
tion of the structure of sarcodictyins A (7) and B (8) reveals
the three branches of possible molecular diversification; those
emanating from skeletal carbons C-3, C-4, and C-8 (see structure
IV, Figure 2 for numbering). Furthermore, the ready availability
of a suitable common intermediate for attachment to a solid
support and the potential reactivity of the functional groups at
C-3, C-4, and C-8 presented an attractive opportunity for the
design and construction of a general sarcodictyin library depicted
under structure I (Figure 2). Thus, compounds I could be
obtained by trans-ketalization with a variety of alcohols with
simultaneous cleavage from the resin II, whereas the latter
structure II could be tailored from III by various functional
group (FG) manipulations at the indicated positions. Structures
III, in turn, could be obtained from IV by ester or carbamate
bond formation. Finally, disconnection of the conjugates IV
unravels possible precursors, sarcodictyin scaffold V, an ap-
propriate linker VI, and resin VII.
Figure 2. Retrosynthetic analysis of a sarcodictyin library (I).
12,10,18,19c and 1410,19c (Scheme 1) were designed and constructed
as shown in Scheme 1. Thus, hydroxymethyl polystyrene resin
9 was reacted with excess glutaric anhydride in the presence of
Et3N, followed by capping with pivaloyl chloride under the same
conditions, to afford resin 10 in >90% overall yield. On the
other hand, reaction of Merrifield resin 11 with excess of the
monosodium alkoxide of 1,4-butanediol resulted in the formation
of resin 12 in 99% yield. Iodination of the latter (12) with I2-
Ph3P-imidazole then furnished iodide 13 (>95% yield) which
was converted to its phosphonium salt by treatment with Ph3P
at 100 °C (95% yield) and hence to phosphorane 14 (>90%
yield) by the action of LiHMDS (for abbreviations, see legends
in schemes). These resins were then ready for coupling with
suitable sarcodictyin scaffolds such as 16-18 and 20 (Scheme
2). The latter compounds were prepared from the previously
synthesized intermediate 1516 as shown in Scheme 2. Thus,
coupling of 15 with ethylene glycol or 1,4-butanediol in the
presence of PPTS resulted in the formation of compounds 16
(91%) and 17 (94%), respectively. On the other hand, acetylation
of 15 furnished 18 (96%) whose reaction with 1,6-hexanediol
in the presence of PPTS led to 19 (92%). Oxidation of 19 with
Dess-Martin reagent20 gave the desired aldehyde 20 in 96%
yield.
Construction of Resins and Substrates for Attachment.
In preparation for a solid phase synthesis of sarcodictyins A
(7) and B (8) and libraries thereof, the functionalized resins 10,
(7) For a comprehensive review, see: Nicolaou, K. C.; Roschangar, F.;
Vourloumis, D. Angew. Chem. Int. Ed. 1998, 37, 2014-2045.
(8) (a) Ho¨fle, G.; Bedorf, N.; Steinmetz, H.; Schomburg, D.; Gerth, K.;
Reichenbach, H. Angew. Chem. Int. Ed. Engl. 1996, 35, 1567-1569. (b)
Bollag, D. M.; McQueney, P. A.; Zhu, J.; Hensens, O.; Koupal, L.; Liesch,
J.; Goetz, M.; Lazarides, E.; Woods, C. M. Cancer Res. 1995, 55, 2325-
2333. (c) Kowalski, R. J.; Giannakakou, P.; Hamel, E. J. Biol. Chem. 1997,
272, 2534-2541. (d) Su, D.-S.; Meng, D.; Bertinato, P.; Balog, A.;
Sorensen, E. J.; Danishefsky, S. J.; Zheng, Y.-H.; Chou, T.-C.; He, S.;
Horwitz, S. B. Angew. Chem. Int. Ed. Engl. 1997, 36, 757-759. (e) Meng,
D.; Su, D.-S.; Balog, A.; Bertinato, P.; Sorensen, E. J.; Danishefsky, S. J.;
Zheng, Y.-H.; Chou, T.-C.; He, L.; Horwitz, S. B. J. Am. Chem. Soc. 1997,
119, 2733-2734. (f) Schinzer, D.; Limberg, A.; Bauer, A.; Bo¨hm, O. M.;
Cordes, M. Angew. Chem. Int. Ed. Engl. 1997, 36, 523-524.
(9) (a) Yang, Z.; He, Y.; Vourloumis, D.; Vallberg, H.; Nicolaou, K. C.
Angew. Chem. Int. Ed. Engl. 1997, 36, 166-168. (b) Nicolaou, K. C.;
Sarabia, F.; Ninkovic, S.; Yang, Z. Angew. Chem. Int. Ed. Engl. 1997, 36,
525-526.
(10) Nicolaou, K. C.; Winssinger, N.; Pastor, J. A.; Ninkovic, S.; Sarabia,
F.; He, Y. Vourloumis, D.; Yang, Z.; Li, T.; Giannakakou, P.; Hamel, E.
Nature (London) 1997, 387, 268-272.
(11) Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggen, P.; McPhail, A.
T. J. Am. Chem. Soc. 1971, 93, 2325-2327.
(12) Nicolaou, K. C.; van Delft, F. L.; Ohshima, T.; Vourloumis, D.;
Xu, J.; Hosokawa, S.; Pfefferkorn, J.; Kim, S.; Li, T. Angew. Chem. Int.
Ed. Engl. 1997, 36, 2520-2524.
Loading of Sarcodictyin Scaffolds onto the Solid Support.
The reaction of sarcodictyin derivatives 16 and 17 with excess
functionalized resin 10 in the presence of Et3N and 4-DMAP
(13) Nicolaou, K. C.; Ohshima, T.; Hosokawa, S.; van Delft, F. L.;
Vourloumis, D.; Xu, J. Y.; Pfefferkorn, J.; Kim, S. J. Am. Chem. Soc. 1998,
120, 8674-8680.
(14) Chen, X.-T.; Bishan, Z.; Bhattacharya, S. K.; Gutteridge, C. E.;
Pettus, C. E.; Thomas, R. R.; Danishefsky, S. J. Angew. Chem. Int. Ed.
1998, 37, 789-792.
(18) Nicolaou, K. C.; Pastor, J.; Winssinger, N. J. Am. Chem. Soc. 1998,
120, 5132-5133.
(19) (a) Nicolaou, K. C.; Xiao, X.-Y.; Parandoosh, Z.; Senyei, A.; Nova,
M. P. Angew. Chem. Int. Ed. Engl. 1995, 34, 2289-2291. (b) Moran, E. J.;
Sarshar, S.; Cargill, J. F.; Shahbaz, MJ. M.; Lio, A.; Mjalli, A. M.;
Armstrong, R. W. J. Am. Chem. Soc. 1995, 117, 10787-10788. (c)
Nicolaou, K. C.; Vourloumis, D.; Li, T.; Pastor, J.; Winssinger, N.; He,
Y.; Ninkovic, S.; Sarabia, F.; Vallberg, H.; Roschangar, F.; King, N. P.;
Finlay, M. R. V.; Giannakakou, P.; Verdier-Pinard, P.; Hamel, E. Angew.
Chem. Int. Ed. Engl. 1997, 36, 2097-2103.
(15) Nicolaou, K. C.; Xu, J.-Y.; Kim, S.; Ohshima, T.; Hosokawa, S.;
Pfefferkorn, J. J. Am. Chem. Soc. 1997, 119, 11353-11354.
(16) Nicolaou, K. C.; Xu, J.; Kim, S.; Pfefferkorn, J.; Ohshima, T.;
Vourloumis, D.; S. Hosokawa, J. Am. Chem. Soc. 1998, 120, 8661-8673.
(17) Nicolaou, K. C.; Kim, S.; Pfefferkorn, J.; Xu, J.-Y.; Ohshima, T.;
Hosokawa, S.; Vourloumis, D.; Li, T. Angew. Chem. Int. Ed. 1998, 37,
1418-1421.

10816 J. Am. Chem. Soc., Vol. 120, No. 42, 1998
Nicolaou et al.
Scheme 1. Synthesis of Resins 10, 12, and 14 for the
resins 23 and 24 in hand, we proceeded to investigate their use
in the synthesis of a sarcodictyin library. As a prelude to a library
construction, and in order to develop the chemistry required
for the operation, we first targeted the naturally occurring
sarcodictyins A (7) and B (8). As demonstrated in Scheme 4,
both resins performed equally well. Thus, NaOMe-induced
deacetylation of 23 or 24 led smoothly to 25 (>95%) which
coupled with mixed anhydride 2612,13,15-17 in the presence of
Et3N and 4-DMAP to afford conjugate 27 in ca. 90% yield.
Desilylation of 27 (>95%), followed by Dess-Martin oxida-
tion20 (>95%), led efficiently to aldehyde 28. Further oxidation
of 28 with NaClO2 (>95%) and esterification of the resulting
carboxylic acid with MeOH or EtOH in the presence of DCC
furnished, in ca. 90% yield, sarcodictyin A and B conjugates
29 and 30 respectively. Finally, generation of the natural
substances (7 and 8) from the corresponding resins was achieved
by exposure to CSA in CH2Cl2:H2O (2:1). The overall yield of
sarcodictyin A (7) was ca. 51% from 24 or 44% from 23 and
of sarcodictyin B (8) was 48% from 24 or 42% from 23. The
spectroscopic properties (1H, 13C NMR, HRMS, RD, IR) of 7
and 8 were identical to those exhibited by authentic samples
previously obtained in these laboratories by a solution total
synthesis.16
Loading of the Sarcodictyin Core on Solid Phasea
a Reagents and conditions: (a) glutaric anhydride (4.0 equiv), Et3N
t
(5.0 equiv), CH2Cl2, 25 °C, 8 h; (b) BuCOCl (3.0 equiv), Et3N (5.0
equiv), CH2Cl2, 25 °C, 6 h, >90% for two steps; (c) 1,4-butanediol
n
(4.0 equiv), NaH (4.0 equiv), BuNI (0.1 equiv), DMF, 25 °C, 15 h,
99%; (d) I2 (4.0 equiv), Ph3P (4.0 equiv), imidazole (4.0 equiv), CH2Cl2,
0 °C, 4 h, >95%; (e) Ph3P (10.0 equiv), 100 °C, 15 h, >95%; (f)
LiHMDS (1.3 equiv), THF, 25 °C, 2 h, >90%. LiHMDS ) lithium
bis(trimethylsilyl)amide; THF ) tetrahydrofuran; b ) polystyrene.
Construction of a Sarcodictyin Combinatorial Library.
The sarcodictyin library shown in Table 1 was constructed by
a combination of solid phase (Scheme 5) and solution (Scheme
6) methods. For the solid-phase chemistry, resin 24 was used
because of its excellent profile in terms of formation, efficiency,
and reactivity performance. Both parallel and combinatorial
techniques were applied, the latter utilizing Radio frequency
Encoded Combinatorial (REC) chemistry.19
Scheme 2. Synthesis of Tethered Sarcoictyin Cores 16-18
and 20a
Thus, individual flasks with resin 25 or IRORI Microkans21
containing resin 25 were utilized to carry out the chemistry
summarized in Scheme 5. Thus, 25 (derived by deacetylation
of 24) was reacted with LG-R1 (acid anhydride, acid chloride,
carboxylic acid, or isocyanate) under the appropriate coupling
conditions to afford a series of esters and cabamates (90-95%)
which were deprotected with TBAF, leading to hydroxy esters
31 (>95%). A portion of the reactant (resin or Microkans, 31)
was treated with LG-R2 (acid anhydride, acid chloride, or
isocyanate) under appropriate coupling conditions to afford, after
PPTS-induced cleavage in the presence of HO-R3 (60-90%),
a series of sarcodictyins 33 via conjugates 32.
A second portion of the reactant 31 was subjected to Dess-
Martin oxidation to afford aldehyde resin 34 in >95% yield.
Further oxidation of 34 with NaClO2 led to carboxylic acid resin
35 (>95%) which was subjected to coupling reactions with
either alcohols [HO-R4] under Mitsunobu conditions or amines
[H2N-R4] under DCC/4-DMAP conditions. The resulting esters
or amides (36) were then exposed to acid (CSA) cleavage
conditions in HO-R3, affording sublibrary 37 (60-90%).
A third portion of the reactant 31 was converted to azide 38
in >95% yield by the action of (PhO)2PON3, DEAD, and Ph3P.
Reduction of the azido group in 38 with Ph3P-H2O gave the
corresponding amine (95%) which was coupled with LG-R5
[anhydride or acid chloride] to afford the amide derivatives 39.
Compounds 40 were then released from the resins 39 by
exposure to PPTS in HO-R3 (60-90%). Each library member
was obtained in ca. 1-5 mg scale and was purified by silica
gel chromatography (flash column or thin layer) or HPLC. The
rather wide range in yield for the cleavage was attributed to
a Reagents and conditions: (a) PPTS (1.0 equiv), diol:CH2Cl2 (2:
1), 25 °C, 2 h, 91% for 1,2-ethanediol, 94% for 1,4-butanediol; (b)
Ac2O (3.0 equiv), pyridine (5.0 equiv), CH2Cl2, 25 °C, 1 h, 96%; (c)
PPTS (1.0 equiv), 1,6-hexanediol (10 equiv), CH2Cl2, 92%; (d) Dess-
Martin periodinane (2.0 equiv), pyridine (5.0 equiv), NaHCO3 (10
equiv), CH2Cl2, 2 h, 96%. PPTS ) pyridinium p-toluenesulfonate.
led, unexpectedly, to conjugates 21 and 22, respectively, in
>95% yield. The surprising fact that derivatives 16 and 17
attached themselves to the resin via their secondary, rather than
primary, hydroxyl groups was evident from the resistance of
21 and 22 to undergo cleavage under acidic conditions and the
ease by which these scaffolds could be recovered under basic
conditions. This led us to the investigate the resins 12 and 14.
Thus, conjugation of 18 to resin 12 was accomplished in the
presence of PPTS to afford 23, but only in 50% yield despite
several attempts to drive the reaction to completion with
dehydrating agents. In contrast, coupling of aldehyde 20 with
resin 14, followed by capping with acetaldehyde, proceeded
smoothly to afford conjugate 24 in >95% yield, making this
resin a more attractive starting point for further chemical studies.
Solid Phase Synthesis of Sarcodictyins A and B. With
(20) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155-4156.
(21) We thank IRORI Quantum Microchemistry, San Diego, CA, for a
gift of an AccuTag-100 instrument and SMART Microreactors (MicroKans
and MicroTubes). K. C. Nicolaou is an advisor of IRORI.

Combinatorial Sarcodictyin Libraries
J. Am. Chem. Soc., Vol. 120, No. 42, 1998 10817
Scheme 3. Loading of Sarcodictyin Cores to Solid Supportsa
a Reagents and conditions: (a) 10 (5.0 equiv), Et3N (10.0 equiv), 4-DMAP (0.5 equiv), CH2Cl2, 25 °C, 8 h, >95%; then MeOH (20 equiv); (b)
12 (10 equiv), PPTS (1.0 equiv), 4 Å MS, CH2Cl2, 25 °C, 48 h, 50%; then MOM-Cl (20 equiv), iPr2NEt (20 equiv), DMF, 25 °C, 24 h; (c) 14 (5.0
equiv), THF, -78 f 25 °C, 4 h, >95%; then CH3CHO (20 equiv). 4-DMAP ) 4-(dimethylamino)pyridine; PPTS ) pyridinium p-toluenesulfonate,
MOM-Cl ) methoxymethyl chloride; DMF ) dimethylformamide; THF ) tetrahydrofuran; b ) polystyrene.
kinetic reasons and/or instability of the individual products to
prolonged exposure to acidic conditions.
two Taxol-resistant lines (1A9PTX10 and 1A9PTX22).24 Ex-
periments showing IC50 values less than 2000 nM in any of the
tested cell lines are tabulated in Table 2. The data reveal a
number of important structure-activity relationships (SARs).
Thus, compounds 60, 73-75, and 85 exhibited superior tubulin
polymerization properties to those of either sarcodictyins A (7)
or B (8). In the cytotoxicity studies compounds 60, 61, 63, 66-
70, 73, 76, 85, and 92 exhibited potencies comparable to or
higher than those of the natural substances (7 and 8). Particularly
striking were the cytotoxicities of compounds 60, 61, 67, 68,
73, 76, 85, and 92 against the Taxol-resistant tumor cell lines.
Interestingly, the tubulin polymerization potencies of some of
these compounds were not always in line with their cytotoxicity
effects (e.g. compounds 61 and 70). These observations suggest
an additional mechanism of action for these compounds such
as DNA alkylation.17
The importance of the C-8 ester side chain became apparent
by a number of substitutions. Thus, replacing the natural
urocanic acid side chain with acetate (compound 107, Table 1)
or phenyl carbamate (compound 101, Table 1) resulted in
complete loss of activity. Likewise, substitution of the hetero-
cycle with a phenyl group while maintaining the R,â-unsaturated
portion of the ester side chain leads to only negligible biological
activity (compound 99, Table 1). Even the more subtle substitu-
tion of the imidazole-derived natural substituent for a pyridine
(compound 48, Tables 1 and 2), a thiazole (compound 49, Tables
1 and 2), or an oxazole (compound 50, Tables 1 and 2) moiety
led to considerable loss of activity, thereby suggesting a role
for both nitrogen atoms of the natural products in their
mechanism of action. In contrast, modifications at the C-4 ketal
center appear more tolerable for biological activity. Thus,
replacement of the OH group of the natural products with an
OMe moiety resulted in enhanced biological activity against
the Taxol-resistant cell lines (compounds 60 and 61, Tables 1
Due to the low yields obtained for the DCC-coupled products
on solid phase, a number of sarcodictyin analogues were
prepared by conventional solution methods. Specifically, sar-
codictyins 42-54 were synthesized as outlined in Scheme 6.
Thus, a number of ester side chains were introduced at C-8 and
the appendage at C-4 was modified to include CH2OH, CH2-
OAc, and CH2F. Thus, DCC/4-DMAP-assisted coupling of 4116
with carboxylic acids Ar-I, Ar-II, and Ar-III (derived from
the corresponding known pyridine, thiazole,22 and oxazole23
aldehydes by a Wittig olefination-saponification sequence in
excellent yields) gave, after TBAF removal of the silyl protect-
ing group, esters 42 (73%), 43 (61%), and 44 (79%), respec-
tively. Dess-Martin oxidation20 of these hydroxy esters led to
aldehydes 45 (44%), 46 (40%), and 47 (84%), respectively.
Further oxidation of 45, 46, and 47 with NaClO2 and treatment
of the resulting carboxylic acids with CH2N2 or CH3CHN2 led
to the formation of sarcodictyins 48 (43%), 49 (71%), and 50
(87%), respectively. The fluorosarcodictyin 5217 was generated
from the previously synthesized compound 5117 by the action
of DAST (99%), whereas acetates 5317 and 54 were prepared
from 51 by sequential treatment with Ac2O/Et3N/4-DMAP and
CSA in CH2Cl2:H2O as indicated in Scheme 6.
Biological Evaluation of Sarcodictyins. The synthesized
sarcodictyin library (shown in Table 1) was screened for
induction of tubulin polymerization using the filtration colori-
metric assay and 100 µM compound at 37 °C (results are listed
in Table 1).8b These investigations were then followed by
cytotoxicity studies with ovarian cancer cells (1A9) including
(22) (a) Nicolaou, K. C.; He, Y.; Vourloumis, D.; Vallberg, H.;
Roschangar, F.; Sarabia, F.; Ninkovic, S.; Yang, Z.; Trujillo, J. J. Am. Chem.
Soc. 1997, 119, 7960-7973. (b) Nicolaou, K. C.; Ninkovic, S.; Sarabia,
F.; Vourloumis, D.; He, Y.; Vallberg, H.; Finlay, M. R. V.; Yang, Z. J.
Am. Chem. Soc. 1997, 119, 7974-7991.
(23) Kende, A. S.; Blass, B. E.; Henry, J. R. Tetrahedron Lett. 1995,
36, 4741-4744.
(24) Giannakakou, P.; Sackett, D. L.; Kang, Y.-K.; Zhan, Z.; Buters, J.
T. M.; Fojo, T.; Poruchynsky, M. S. J. Biol. Chem. 1995, 272, 17118-
17125.
(25) Present work.

10818 J. Am. Chem. Soc., Vol. 120, No. 42, 1998
Nicolaou et al.
Scheme 4. Solid Phase Synthesis of Sarcodictyins A (7) and
B (8)a
these compounds as compared to the natural products. Thus,
substitution of the methyl (compound 60, Tables 1 and 2) with
an ethyl (compound 61, Tables 1and 2), n-propyl (compound
68, Tables 1 and 2), or allyl group (compound 70, Tables 1
and 2) resulted in enhancement of the biological activity. A
reversal of the trend was noted with bulkier substituents, such
as n-butyl (compound 63, Tables 1 and 2) or isopentyl
(compound 71, Tables 1 and 2). Interestingly, however, the
bulky moieties of anthracenyl (compound 92, Tables 1 and 2),
benzyloxyethyl (compound 69, Tables 1 and 2), and 4-butyl-
phenyl (compound 66, Tables 1 and 2) exhibited cytotoxicity
comparable to, or better than, the natural products (even though
their tubulin polymerization potencies were modest).
Figure 3 summarizes the SARs so far obtained within the
sarcodictyin family of compounds.
Experimental Section
General Information. See the Supporting Information for general
techniques. Substituted polystyrene resins (100-200 mesh, 1% DVB)
were purchased from Novabiochem. All equipment utilized for the REC
microchemistry is commercially available and can be purchased from
IRORI Quantum Microchemistry, La Jolla, CA. The REC chemistry
was carried out according to the recommendations provided by the
manufacturer. All reactions carried out on solid phase were monitored
by TLC analysis of the product obtained upon acidic cleavage from
the resin. Unless otherwise stated, yields of solid phase reactions refer
to the estimated conversion of the reaction precursor based on TLC
analysis. Full experimental data are presented for compounds which
were previously synthesized in solution and thus were fully character-
ized. All compounds obtained from solid phase chemistry, and which
were biologically tested, were characterized by 1H NMR spectroscopy
and mass spectroscopy (see below and Supporting Information for data).
Synthesis of Mixed Anhydride Resin 10. A suspension of hy-
droxymethyl polystyrene resin (5.00 g, 4.00 mmol, 1.0 equiv) in CH2-
Cl2 (50 mL) at 25 °C was treated with Et3N (2.79 mL, 20.0 mmol, 5.0
equiv) and glutaric anhydride (1.87 g, 16.0 mmol, 4.0 mmol). The
reaction mixture was stirred gently (<300 rpm) over 8 h at 25 °C after
which time it was poured into a fritted funnel, washed with CH2Cl2
(50 mL), MeOH (50 mL), CH2Cl2 (3 × 50 mL), and ether (2 × 200
mL), and dried to constant weight under high vacuum. The resulting
resin was resuspended in CH2Cl2 (50 mL) at 25 °C and treated with
Et3N (2.79 mL, 20.0 mmol, 5.0 equiv) followed by pivaloyl chloride
(1.44 g, 12.0 mmol, 3.0 equiv). The reaction mixture was stirred gently
over 6 h at 25 °C after which time it was poured into a fritted funnel,
washed with the following distilled solvents under an argon atmo-
sphere: CH2Cl2 (50 mL), Et2O (50 mL), CH2Cl2 (3 × 50 mL), and
Et2O (2 × 200 mL), and dried to constant weight under high vacuum
(5.60 g). A two-step yield of >90% was determined by titration of the
mixed anhydride resin with benzyl alcohol. Thus, in three separate
experiments, the mixed anhydride resin (300 mg, 0.207 mmol, 1.0
equiv) was treated with benzyl alcohol (15.6 mg, 0.145 mmol, 0.7 equiv;
20.1 mg, 0.186 mmol, 0.9 equiv; and 24.5 mg, 0.227 mmol, 1.1 equiv)
followed by Et3N (43.2 µL, 0.310 mmol, 1.5 equiv) and 4-DMAP (5.0
mg, 0.041 mmol, 0.2 equiv). TLC analysis of the reaction mixtures
revealed complete consumption of the benzyl alcohol for the experi-
ments with 0.7 and 0.9 equiv of benzyl alcohol establishing the yield
as at least 90%.
a Reagents and conditions: (a) NaOMe (5.0 equiv), MeOH:THF (1:
3), 25 °C, 12 h, >95%; (b) 26 (5.0 equiv), Et3N (10 equiv), 4-DMAP
(2.0 equiv), CH2Cl2, 25 °C, 48 h, ca. 90%; (c) TBAF (10 equiv), THF,
25 °C, 8 h, >95%; (d) Dess-Martin periodinane (5.0 equiv), NaHCO3
(15 equiv), pyridine (15 equiv), CH2Cl2, 25 °C, 2 h, 95%; (e) NaClO2
(12 equiv), NaH2PO4 (12 equiv), 2-methyl-2-butene (50 equiv), THF-
BuOH:H2O (5:5:1) 25 °C, 48 h, >95%; (f) MeOH (10 equiv), DCC
(10 equiv), 4-DMAP (5.0 equiv), DMF, 25 °C, 48 h, ca. 90%; (g) CSA
(3.0 equiv), CH2Cl2:H2O (2:1), 25 °C, 40 h, ca. 75%. Overall yield for
sarcodictyin A: ca. 51% from 24 and ca. 44% from 23. Overall yield
of sarcodictyin B: ca. 48% from 24 and ca. 42% from 23. 4-DMAP
) 4-(dimethylamino)pyridine; TBAF ) tetra-n-butylammonium fluo-
ride; DCC ) dicyclohexylcarbodiimide; THF ) tetrahydrofuran; b )
polystyrene; CSA ) camphorsulfonic acid.
and 2), whereas substitution with OnPr or OCH2CF3 resulted in
an overall decrease of cytotoxicity (compounds 74 and 84,
Tables 1 and 2). The C-15 reduced compound and derivatives
thereof (e.g. compounds 51-53 and 55-59, Tables 1 and 2)
failed to exhibit strong tubulin polymerization or cytotoxicity
properties, which is rather intriguing, given the potent biological
actions of eleutherobin (4) whose C-15 position is reduced and
glycosylated.
Interestingly, the C-15 dimethyl acetal (compound 73, Tables
1 and 2) displayed biological activities comparable to those of
the natural products (7 and 8, Tables 1 and 2), thus demonstrat-
ing that ester functionality is not a requirement for activity.
Modification of the alcohol component of the C-3 ester group
resulted in significant modulation of the biological actions of
Synthesis of Hydroxy Resin 12. To a suspension of NaH (60% in
mineral oil, 1.76 g, 44.0 mmol, 4.0 equiv) in DMF (100 mL) at 0 °C
was added 1,4-butanediol (3.86 mL, 44.0 mmol, 4.0 equiv), and the
reaction mixture was stirred for 1 h at 0 °C. Merrifield resin (10.0 g,
11.0 mmol, 1.0 equiv) was then added to the reaction mixture followed
by tetra-n-butylammonium iodide (400 mg, 0.11 mmol, 0.1 equiv), and
the mixture was stirred gently (<300 rpm) over 12 h. The resin was
poured into a fritted funnel, washed with aq HCl (1 N, 200 mL), DMF
(2 × 300 mL), MeOH (200 mL), CH2Cl2 (300 mL), MeOH (200 mL),
CH2Cl2 (2 × 300 mL), and Et2O (2 × 200 mL), and dried to constant
weight under high vacuum (9.98 g, 99% yield). A sample of this resin
was suspended in CH2Cl2 at 25 °C and treated with Fmoc-Cl (5.0 equiv)

Combinatorial Sarcodictyin Libraries
J. Am. Chem. Soc., Vol. 120, No. 42, 1998 10819
Table 1. Structures and Tubulin Polymerization Properties of Sarcodictyin Analogues
a See legend of Table 2.
and pyridine (5.0 equiv) for 6 h. The reactive hydroxyl groups were
photometrically quantified from the amount of Fmoc chromophore
released upon treatment of the Fmoc-resin with 10% Et3N in CH2Cl2
at 25 °C for 8 h.

10820 J. Am. Chem. Soc., Vol. 120, No. 42, 1998
Nicolaou et al.
Scheme 5. Synthesis of a Sarcodictyin Library on Solid Phasea
a Reagents and conditions: (a) NaOMe (5.0 equiv), MeOH:THF (1:3), 25 °C, 12 h, >95%; (b1) LG-R1 (5.0 equiv), Et3N (10 equiv), 4-DMAP
(2.0 equiv), DMF, 50 °C, 48 h, 90-95%; (b2) LG-R1 (10 equiv), DCC (10 equiv), 4-DMAP (2.0 equiv), DMF, 50 °C, 48 h, 90-95%; (c) TBAF
(10 equiv), THF, 25 °C, 8 h, >95%; (d) LG-R2 (10 equiv), Et3N (10 equiv), 4-DMAP (2.0 equiv), CH2Cl2, 25 °C, 20 h, 70-95%; (e) PPTS (3.0
equiv), MeOH, 25 °C, 24 h, 60-90%; (f) Dess-Martin periodinane (5.0 equiv), NaHCO3 (15 equiv), pyridine (15 equiv), CH2Cl2, 25 °C, 2 h, 95%;
(g) NaClO2 (25 equiv), KH2PO4 (25 equiv), 2-methyl-2-butene (50 equiv), THF:tBuOH:H2O (5:5:1) 25 °C, 48 h, >95%; (h) HO-R4 (10 equiv),
DEAD (10 equiv), Ph3P (10 equiv), THF, 0 f 25 °C, 12 h, >95%; (i) H2N-R4 (10 equiv), DCC (10 equiv), 4-DMAP (5 equiv), DMF, 25 °C, 20
h, >95%; (j) CSA (3.0 equiv), HO-R3, 25 °C, 15 h, 60-90%; (k) (PhO)2PON3 (10 equiv), DEAD (10 equiv), Ph3P (10 equiv), THF, 0 f 25 °C,
4 h, >95%; (l) Ph3P (10 equiv), H2O (30 equiv), THF, 25 °C, 8 h, >95%; (m) LG-R5 (10 equiv), Et3N (15 equiv), CH2Cl2, 25 °C, 10 h, >90%.
LG ) leaving group; 4-DMAP ) 4-(dimethylamino)pyridine; TBAF ) tetra-n-butylammonium fluoride; DEAD ) diethyl azodicarboxylate; DCC
) dicyclohexylcarbodiimide; THF ) tetrahydrofuran; DMF ) dimethylformamide; b ) polystyrene; CSA ) camphorsulfonic acid; PPTS )
pyridinium p-toluenesulfonate.

Combinatorial Sarcodictyin Libraries
J. Am. Chem. Soc., Vol. 120, No. 42, 1998 10821
Table 2. Cytotoxicity Data of Sarcodictyins and Related
Compounds
Scheme 6. Synthesis of Sarcodictyin Analogues 48-54 in
solutiona
inhibition of carcinoma cell
growth,b IC50 (nM)
% tubulin
compd no.
1 Taxol
2 epothilone A
3 epothilone B
7 sarcodictyin A
polymerizationa
1A9
1A9PTX10 1A9PTX22
65
73
97
67
71
18
42
4
37
27
37
34
47
30
72
46
61
40
30
38
52
69
54
51
4
74
47
75
52
85
28
20
22
26
48
2
2
0.04
240
2
50
19
0.035
140
160
1800
244
40
4
0.04
360
80
8 sarcodictyin B
48
49
50
51
52
53
54
56
58
60
61
62
63
64
66
67
68
69
70
72
73
74
75
76
85
86
87
88
89
92
430
300
>2000
800
1850
1050
1400
>2000
800
70
>2000
180
385
>2000
>2000
1620
>2000
1800
1200
84
800
>2000
>2000
>2000
>2000
>2000
1600
4
2
360
95
200
110
25
3
80
9
600
30
1
60
1210
85
350
90
35
4
91
12
400
540
100
290
120
31
5
85
10
600
60
1800
700
60
160
440
1000
1400
900
130
45
>2000
500
45
110
110
500
1400
640
110
>2000
1400
65
13
400
1240
1300
1300
90
a The tubulin polymerization measurements were performed at 37
°C as described elsewhere8b,19c except for adjustments in drug concen-
tration (100 µM) and incubation time (90 min). b The cytotoxicity
experiments were carried out as previously described.19c,24
a Reagents and conditions: (a) acid Ar-I or Ar-II or Ar-III (1.3
equiv), DCC (2.0 equiv), 4-DMAP (0.5 equiv), CH2Cl2, 25 °C, 36 h;
(b) TBAF (2.0 equiv), THF, 25 °C, 1 h, 73% for 42 over two steps,
61% for 43 over two steps, 79% for 44 over two steps; (c) Dess-
Martin periodinane (2.5 equiv), NaHCO3 (ca. 10 equiv), CH2Cl2, 25
°C, 0.5 h, 44% for 45, 40% for 46, 84% for 47; (d) NaClO2 (6.0 equiv),
NaH2PO4 (3.0 equiv), 2-methyl-2-butene (50 equiv), THF:tBuOH:H2O
(5:5:1), 0 °C, 2 h; (e) CH2N2 or CH3CHN2, 0 °C, 10 min, 43% for 48
over two steps, 71% for 49 over two steps, 87% for 50 over two steps;
(f) Ac2O (5.2 equiv), Et3N (6.8 equiv), 4-DMAP (1.6 equiv), CH2Cl2,
25 °C, 2 h, 100%; (g) CSA (cat., 10% mol), CH2Cl2:H2O (10:1), 25
°C, 72 h, 95%; (h) DAST (2.0 equiv), CH2Cl2, -78 °C, 3 h, 99%; (i)
Ph3PCHCO2Me (1.5 equiv), benzene, 80 °C, 95-98%; (j) LiOH (3.0
equiv), THF:H2O (1:1). 25 °C, 100%. DCC ) dicyclohexylcarbodi-
imide; 4-DMAP ) 4-(dimethylamino)pyridine; TBAF ) tetra-n-
butylammonium fluoride; THF ) tetrahydrofuran; CSA ) camphor-
sulfonic acid; DAST ) diethylaminosulfur trifluoride.
Figure 3. Structure activity relationships (SARs) of sarcodictyins: (a)
replacement of side chain with acetate, phenyl carbamate, or cynamoyl
ester is not tolerated; (b) replacement of the substituted imidazole
heterocycle by a pyridine, thiazole, or oxazole led to reduced activity;
(c) methyl and ethyl ketals are well tolerated, whereas propyl or
trifluoroethyl ketals are not; (d) esters are more active than the
corresponding amides; substitution of the ester group is well tolerated;
reduction of the ester to the alcohol and derivatives thereof are not
tolerated (except for the eleutherobin 4).
sequentially with imidazole (2.55 g, 37.6 mmol, 4.0 equiv), Ph3P (9.85
g, 37.6 mmol, 4.0 equiv), and iodine (9.55 g, 37.6 mmol, 4.0 equiv).
The reaction mixture was stirred gently at 0 °C for 4 h after which
time it was poured into a fritted funnel, washed with CH2Cl2 (3 × 200
mL), MeOH (200 mL), CH2Cl2 (2 × 200 mL), and Et2O (2 × 200
Synthesis of Iodo Resin 13. A suspension of hydroxy resin 12 (9.00
g, 9.39 mmol, 1.0 equiv) in CH2Cl2 (100 mL) at 0 °C was treated

10822 J. Am. Chem. Soc., Vol. 120, No. 42, 1998
Nicolaou et al.
mL), and dried to constant weight under high vacuum (9.95 g, >95%
yield). Subjection of this resin to the Fmoc assay described in the
synthesis of 12 indicated complete consumption of the alcohol.
Synthesis of Phosphorane Resin 14. A mixture of iodide resin 13
(5.00 g, 4.45 mmol, 1.0 equiv) and Ph3P (11.7 g, 44.5 mmol, 10 equiv)
in DMF (30 mL) was gently stirred at 100 °C for 15 h after which
time it was poured into a fritted funnel, washed with warm (100 °C)
DMF (3 × 200 mL), CH2Cl2 (2 × 200 mL), and Et2O (3 × 300 mL)
and dried to a constant weight of 6.10 g (>95% yield based on mass
gain). A portion of this resin (2.2 g, 1.57 mmol, 1.0 equiv) was
resuspended in THF (15 mL) at 25 °C, LiHMDS (1.0 M in THF, 2.04
mL, 2.04 mmol, 1.3 equiv) was added, and the reaction was allowed
to stir for 2 h at ambient temperature after which time the resin adopted
a deep red color. The supernatant solvent was removed by cannulation,
the resin was washed with THF (3 × 15 mL), and the resulting resin
was used for the next step without any additional treatment (>90%
yield). The yield was determined as follows. The ylide was quenched
with benzaldehyde (5.0 equiv, 25 °C, 6 h), and the resulting resin was
subjected to ozonolysis (CH2Cl2, -78 °C, 30 min) followed by a
reductive workup (Me2S). The quantity of benzaldehyde recovered was
quantified by HPLC absorption calibrated with an authentic benzal-
dehyde sample.
mixture was removed from the cold bath after 15 min and stirred for
an additional 2 h at 25 °C after which time TLC analysis indicated
complete reaction. The crude mixture was loaded onto a short silica
gel column and eluted with EtOAc-hexane (1:3) to yield pure product
20 (0.430 g, 96% yield). Rf ) 0.18 (silica gel, EtOAc-hexane, 1:3);
[R]25 +29.0 (c ) 1.0, C6H6); FT-IR (neat) νmax 2940, 2865, 1939,
D
1458, 1369 cm-1; 1H NMR (500 MHz, C6D6) δ 9.33 (t, J ) 1.5 Hz, 1
H), 6.13 (d, J ) 6.0 Hz, 1 H), 6.08 (d, J ) 9.0 Hz, 1 H), 6.01 (d, J )
6.0 Hz, 1 H), 5.41 (bs, 1 H), 5.08 (d, J ) 6.0 Hz, 1 H), 4.53 (d, J )
13.0 Hz, 1 H), 4.48 (d, J ) 13.0 Hz, 1 H), 4.35 (m, 1 H), 3.55 (m, 2
H), 2.90 (m, 1 H), 2.59 (m, 1 H), 2.31 (m, 1 H), 1.92-1.56 (m, 2 H),
1.82 (dd, J ) 12.5, 1.5 Hz, 2 H), 1.73 (s, 3 H), 1.70 (s, 3 H), 1.63 (m,
1 H), 1.51 (s, 3 H), 1.50-1.20 (m, 9 H), 1.16 (s, 21 H), 1.08 (d, J )
6.5 Hz, 3 H), 0.91 (d, J ) 6.5 Hz, 3 H); 13C NMR (125 MHz, C6D6)
δ 200.2, 168.7, 137.2, 134.1, 133.2, 131.3, 130.2, 121.6, 116.0, 89.6,
81.9, 65.6, 65.2, 61.6, 43.5, 42.9, 39.0, 33.8, 31.9, 29.7, 29.1, 25.9,
24.9, 24.4, 22.1, 22.0, 21.7, 20.5, 20.4, 18.0, 15.3, 12.1; HRMS (FAB)
calcd for C37H62O6Si (M + Cs+): 763.3370, found 763.3390.
Attachment of Sarcodictyin Core 18 on Resin 12 by Transket-
alization. To a suspension of resin 12 (0.563 g, 0.54 mmol, 10 equiv)
in CH2Cl2 (3 mL) containing flamed-dried 4 Å molecular sieves (0.30
g) at 25 °C was added a solution of ketal 18 (28 mg, 0.054 mmol, 1.0
equiv) in CH2Cl2 (1 mL) followed by PPTS (13 mg, 0.054 mmol, 1.0
equiv). The reaction mixture was agitated gently on a wrist shaker at
ambient temperature for 48 h and then filtered and washed with
anhydrous CH2Cl2 (2 × 5 mL). The unreacted starting material in the
combined filtrates was purified to recover 14 mg of pure 18 (50% yield
based on recovered starting material). The excess alcohol on the resin
was capped by resuspending the resin in DMF (3 mL) followed by
addition of MOM-Cl (88 mg, 0.054 mmol, 20 equiv) and iPr2NEt (126
mg, 1.1 mmol, 20 equiv) for 24 h at ambient temperature. The resin
was filtered in a fritted funnel, washed with CH2Cl2 (3 × 50 mL)
containing 1% Et3N, and Et2O (2 × 50 mL), and dried under high
vacuum to a constant weight of 0.56 g (0.039 mmol/g loading of the
sarcodictyin core).
Attachment of Sarcodictyin Core 20 on Resin 14 by a Wittig
Reaction. To a suspension of ylide 14 (0.75 mmol, 7.0 equiv) in THF
(2 mL) cooled to -78 °C was added a solution of aldehyde 20 (67.6
mg, 0.107 mmol, 1.0 equiv) in THF (5 mL). The reaction mixture was
allowed to warm slowly to ambient temperature over 2 h and was stirred
for an additional 2 h at 25 °C, after which time TLC analysis indicated
complete consumption of the aldehyde (>95% yield). The excess ylide
was quenched by the addition of acetaldehyde (99 mg, 2.25 mmol, 21
equiv), and the resin was collected on a fritted funnel, washed with
THF (3 × 50 mL) containing 1% Et3N, and Et2O (2 × 50 mL), and
dried under high vacuum to a constant weight of 836 mg (0.128 mmol/g
loading of the sarcodictyin core). In a cleavage demonstration experi-
ment, a sample of this resin (225 mg, 28.8 µmol, 1.0 equiv) was treated
with PPTS (14.3 mg, 57.6 µmol, 2.0 equiv) in MeOH (0.5 mL) at 25
°C for 30 h to recover, after purification (silica gel, flash column
chromatography), 14.2 mg of the corresponding methyl ketal (90% for
two steps).
Acetate 18. A solution of hydroxy compound 15 (0.404 g, 0.806
mmol, 1.0 equiv) in CH2Cl2 (10 mL) at 25 °C was treated with pyridine
(0.322 g, 4.03 mmol, 5.0 equiv) and Ac2O (0.246 g, 2.42 mmol, 3.0
equiv). The reaction mixture was stirred for 1 h at 25 °C after which
time TLC analysis indicated complete reaction. The reaction mixture
was poured into Et2O (150 mL), washed with saturated aqueous
NaHCO3 (3 × 100 mL), dried over MgSO4, and concentrated. The
crude mixture was purified by flash column chromatography (silica
gel, EtOAc-hexane, 1:3) to furnish pure acetate 18 (0.421 g, 96%
yield). Rf ) 0.20 (silica gel, EtOAc-hexane, 1:3); [R]25 +47.8 (c )
D
2.32, CHCl3); FT-IR (neat) νmax 2942, 2866, 2363, 2334, 1739, 1720,
1459, 1364 cm-1; 1H NMR (500 MHz, CDCl3) δ 6.11 (d, J ) 7.5 Hz,
1 H), 6.03 (d, J ) 7.5 Hz, 1 H), 5.43 (d, J ) 11.5 Hz, 1 H), 5.23 (bs,
1 H), 5.07 (s, 1 H), 4.66 (d, J ) 9.0 Hz, 1 H), 4.37 (d, J ) 9.0 Hz, 1
H), 4.06 (d, J ) 9.5 Hz, 1 H), 3.99 (m, 1 H), 2.55 (m, 1 H), 2.27 (m,
1 H), 2.05 (s, 3 H), 1.99 (m, 1 H), 1.60-1.49 (m, 3 H), 1.51 (s, 3 H),
1.45 (s, 3 H), 1.36-1.25 (m, 1 H), 1.04 (s, 21 H), 0.93 (d, J ) 7.0 Hz,
3 H), 0.90 (d, J ) 7.0 Hz, 3 H); 13C NMR (125 MHz, CDCl3) δ 170.1,
135.6, 134.2, 134.1, 132.7, 132.0, 121.3, 112.5, 89.9, 81.5, 68.5, 42.2,
38.5, 33.9, 31.5, 28.9, 25.5, 24.4, 22.2, 22.0, 21.3, 20.5, 17.9, 11.7;
HRMS (FAB) calcd for C32H52O5Si (M + Cs+): 665.2638, found
665.2615.
Hydroxy Ketal 19. A solution of ketal 18 (0.421 g, 0.774 mmol,
1.0 equiv) in CH2Cl2 (5 mL) at 25 °C was treated with 1,6-hexanediol
(0.913 g, 7.74 mmol, 10 equiv) and PPTS (0.194 g, 0.774 mmol, 1.0
equiv). The reaction mixture was stirred for 4 h at 25 °C after which
time TLC analysis indicated complete reaction. The reaction mixture
was loaded onto a short silica column and eluted with EtOAc-hexanes
(1:2) to give pure hydroxy ketal 19 (0.450 g, 92% yield). Rf ) 0.15
(silica gel, EtOAc-hexanes, 1:2); [R]25 +36.5 (c ) 1.0, C6H6); FT-
D
1
IR (neat) νmax 3427, 2936, 2864, 1742, 1465, 1368 cm-1; H NMR
Hydrolysis of Acetate 24 and Formation of Polymer-Bound
Alcohol 25. To a suspension of resin 24 (3.12 g, 0.40 mmol, 1.0 equiv)
in THF (20 mL) was added NaOMe (0.5 M in MeOH, 4.0 mL, 2.0
mmol, 5.0 equiv). The reaction mixture was agitated on a wrist shaker
for 12 h at ambient temperature. The resin was filtered and washed
with MeOH containing 1% Et3N (100 mL), CH2Cl2 containing 1% Et3N
(100 mL), and Et2O (100 mL) and then dried under high vacuum. NMR
analysis of the crude product obtained from the cleavage showed a
single compound corresponding to the previously reported product 41
(Scheme 6) thereby establishing a yield of >95%. Although exact
procedures for the sequence of reactions leading to sarcodictyins A
(7) and B (8) are given only for resin 24, similar procedures were
followed for resin 23 and with similar results.
(500 MHz, C6D6) δ 6.15 (d, J ) 6.0 Hz, 1 H), 6.09 (d, J ) 9.0 Hz, 1
H), 6.05 (d, J ) 6.0 Hz, 1 H), 5.43 (bs, 1 H), 5.08 (dd, J ) 9.0, 1.0
Hz, 1 H), 4.54 (d, J ) 13.0 Hz, 1 H), 4.49 (d, J ) 13.0 Hz, 1 H), 4.37
(m, 1 H), 3.55 (m, 2 H), 3.39 (t, 2 H), 2.90 (m, 1 H), 2.58 (m, 1 H),
2.06 (m, 1 H), 1.91-1.86 (m, 2 H), 1.73 (s, 3 H), 1.69 (s, 3 H), 1.67-
1.53 (m, 3 H), 1.52 (s, 3 H), 1.42-1.36 (m, 6 H), 1.28-1.25 (m, 1 H),
1.18 (s, 21 H), 1.08 (d, J ) 7.0 Hz, 3 H), 0.90 (d, J ) 7.0 Hz, 3 H);
13C NMR (125 MHz, C6D6) δ 169.0, 137.0, 134.3, 133.1, 131.5, 130.2,
121.6, 116.0, 89.6, 81.9, 65.2, 62.3, 61.9, 42.9, 39.0, 33.8, 32.9, 32.0,
30.0, 29.11, 26.3, 25.6, 24.9, 24.5, 22.1, 22.0, 20.5, 20.4, 18.0, 12.1;
HRMS (FAB) calcd for C37H64O6Si (M + Cs+): 765.3527, found
765.3548.
Aldehyde Ketal 20. To a solution of Dess-Martin periodinane
(0.451 g, 1.07 mmol, 1.5 equiv) in CH2Cl2 (10 mL) at 25 °C were
added pyridine (0.280 g, 3.56 mmol, 5.0 equiv) and NaHCO3 (0.598
g, 7.12 mmol, 10 equiv). The mixture was stirred for 15 min at ambient
temperature and then cooled to 0 °C. Alcohol 19 (0.450 g, 0.712 mmol,
1.0 equiv) was added as a solution in CH2Cl2 (10 mL). The reaction
Attachment of the Urocanic Acid Side Chain and Synthesis of
Resin 27. A suspension of hydroxy resin 25 (2.0 g, 0.256 mmol, 1.0
equiv) in DMF (6 mL) was treated with mixed anhydride 26 (0.302 g,
1.28 mmol, 5.0 equiv) in the presence of Et3N (0.357 mL, 2.56 mmol,
10 equiv) and 4-DMAP (62 mg, 0.512 mmol, 2.0 equiv) for 24 h at 50
°C. The resin was filtered, washed with CH2Cl2 containing 1% Et3N

Combinatorial Sarcodictyin Libraries
J. Am. Chem. Soc., Vol. 120, No. 42, 1998 10823
(2 × 25 mL), Et2O (25 mL), CH2Cl2 containing 1% Et3N (2 × 25
mL), and Et2O (3 × 20 mL), and then dried under high vacuum. TLC
analysis after cleavage of the product from the resin by the action of
PPTS (ca. 3 equiv) and MeOH also revealed the presence of 5-10%
of a less polar byproduct presumed to be derived from impurities in
reagent 26. NMR analysis of the crude product obtained from the
cleavage confirmed its identity16 and led to an estimated yield of 90%.
Desilylation and Oxidation of Alcohol 27. Synthesis of Solid-
Supported Aldehyde 28. A suspension of resin 27 (300 mg, 38.4 µmol,
1.0 equiv) in THF (1.5 mL) was treated with TBAF (1.0 M in THF,
384 µmol, 10 equiv) for 8 h at 25 °C. The resin was filtered, washed
with THF containing 1% Et3N (4 × 10 mL) and Et2O (3 × 10 mL),
and then dried under high vacuum. NMR analysis of the crude product
so obtained confirmed its identity16 and established a yield of >95%
for the deprotection steps. The resin (250 mg, 32 µmol, 1.0 equiv) was
resuspended in CH2Cl2 (1.0 mL) containing pyridine (12.8 mg, 160
µmol, 5.0 equiv) and treated with a preformed suspension of Dess-
Martin periodinane (67.2 mg, 160 µmol, 5.0 equiv), NaHCO3 (40.3
mg, 480 µmol, 15 equiv), and pyridine (25.6 mg, 64 µmol, 10 equiv)
in CH2Cl2 (1.5 mL). The mixture mixture was allowed to react for 2 h
at ambient temperature. The resin was then filtered, washed with CH2Cl2
(4 × 10 mL), H2O (3 × 10 mL), MeOH (2 × 5 mL), CH2Cl2 (2 × 5
mL), and Et2O (3 × 5 mL), and dried under high vacuum. The
completion of the reaction, the identity of the resulting product, and
the yield of the reaction (>95%) were established by TLC and NMR
analysis after subjecting a sample the resin to cleavage with CSA (ca.
3 equiv) and MeOH.
Oxidation of Aldehyde 28 and Esterification of the Resulting
Carboxylic Acid. Synthesis of Polymer-Bound Sarcodictyins A (29)
and B (30). A mixture of resin 28 (220 mg, 28.2 µmol, 1.0 equiv),
sodium chlorite (63.3 mg, 704 µmol, 25 equiv), KH2PO4 (83.7 mg,
704 µmol, 25 equiv), and isobutylene (2 M in THF, 1.40 mmol, 50
equiv) in THF:tBuOH:H2O (4:4:1) was allowed to react for 48 h at
ambient temperature (>95% conversion). The resulting resin was
filtered, washed with water (3 × 10 mL), MeOH (2 × 10 mL), 0.5 M
PPTS in CH2Cl2 (3 × 10 mL), CH2Cl2 (2 × 10 mL), and Et2O (2 × 10
mL), and then dried under high vacuum. The resin was then split into
two portions (100 mg each, 12.8 µmol, 1.0 equiv) and each was treated
with a solution of DMF (0.5 mL) containing DCC (26 mg, 128 µmol,
10 equiv) and 4-DMAP (7.7 mg, 64 µmol, 5.0 equiv). To the first
portion of resin was added MeOH (4.0 mg, 128 µmol, 10 equiv), and
to the second portion of resin was added EtOH (5.9 mg, 128 µmol, 10
equiv). The reaction vessels were agitated on a wrist shaker for 48 h
after which time each resin was filtered, washed with CH2Cl2 (4 × 5
mL), MeOH (2 × 5 mL), CH2Cl2 (3 × 5 mL), and Et2O (3 × 5 mL),
and dried under high vaccum (>90% estimated yield).
mmol, 10 equiv), DCC (52 mg, 0.26 mmol, 10 equiv), and 4-DMAP
(6.3 mg, 0.052 mmol, 2.0 equiv), and the reaction mixture was heated
at 50 °C for 48 h. The resin was then filtered, washed with CH2Cl2
containing 1% Et3N (5 × 20 mL), and Et2O (2 × 100 mL), and then
dried under high vacuum (90-95% estimated yield).
Reaction of Alcohol 25 with Phenyl Isocyanate. Toward the
Synthesis of Phenyl Carbamate 31. To a suspension of resin 25 (500
mg, 0.064 mmol, 1.0 equiv) in DMF (4.0 mL) were added phenyl
isocyanate (77 mg, 0.64 mmol, 10 equiv) and 4-DMAP (39 mg, 0.32
mmol, 5 equiv), and the reaction mixture was shaken on a wrist shaker
for 10 h. The resin was filtered, washed with CH2Cl2 containing 1%
Et3N (3 × 15 mL), and Et2O (2 × 15 mL), and then dried under high
vacuum (>95% estimated yield).
General Desilylation Procedure. Synthesis of Hydroxy Resins 31.
A suspension of the silylated resin (1.0 equiv) in THF was allowed to
react with TBAF (10 equiv, 1.0 M in THF) at 25 °C for 6 h. The resin
was then filtered, washed with THF containing 1% Et3N, CH2Cl2
(containing 1% Et3N), and Et2O, and then dried under high vacuum
(>95% estimated yield).
General Procedure for the Functionalization of Hydroxy Resins
31. Synthesis of Compounds 32. A suspension of resin 31 (1.0 equiv)
in CH2Cl2 at 25 °C was treated with Et3N (10 equiv), 4-DMAP (2.0
equiv), and acetic anhydride (10 equiv) or benzoyl chloride (10 equiv)
or methyl chloroformate (10 equiv) or phenylisocyanate (10 equiv).
After 15 h, the resin was filtered, washed with CH2Cl2 containing 1%
Et3N, and Et2O, and then dried under high vacuum. The acylation,
benzoylation, and formation of carbamate were found to proceed
smoothly (>95%) whereas the carbonate formation proceeded in 70%
yield along with the formation of two less polar unidentified byproducts.
General Procedure for the Dess-Martin Oxidation of Solid-
Supported Hydroxy Resins 31. Synthesis of Aldehyde Resins 34.
To a suspension of hydroxy resin 31 (1.0 equiv) in CH2Cl2 containing
pyridine (5.0 equiv) was added a preformed suspension of Dess-Martin
periodinane (5.0 equiv), NaHCO3 (15 equiv), and pyridine (10 equiv)
in CH2Cl2. The mixture was allowed to react for 2 h at ambient
temperature. The resin was then filtered, washed with CH2Cl2, H2O,
MeOH, and Et2O, and dried under high vacuum (>95% estimated
yield).
General Procedure for the Sodium Chlorite Oxidation of Alde-
hyde Resins 34. Synthesis of Carboxylic Acids 35. A mixture of
aldehyde resin 34 (1.0 equiv), sodium chlorite (25 equiv), KH2PO4 (25
equiv), and isobutylene (2 M in THF, 50 equiv) in THF:tBuOH:H2O
(4:4:1) was allowed to react for 48 h at ambient temperature. The
resulting resin was filtered, washed with water, MeOH, 0.5 M PPTS
in CH2Cl2, CH2Cl2, and Et2O, and dried under high vacuum (>95%
estimated yield).
Cleavage of Polymer-Bound Sarcodictyins A an B with CSA/
H2O. Synthesis of Sarcodictyins A (7) and B (8). A suspension of
resin 29 (92 mg, 11.7 µmol, 1.0 equiv) or 30 (90 mg, 11.5 µmol, 1.0
equiv) in CH2Cl2/H2O (2:1, 2.0 mL) at 25 °C was treated with CSA (8
mg, 35.1 µmol, 3.0 equiv) and stirred vigorously over the course of 40
h. The reaction mixture was then quenched with NaHCO3 (9.8 mg,
117 µmol, 10 equiv) and filtered and the aqueous layer washed with
CH2Cl2 (3 × 1 mL). The combined organic layers were dried over
MgSO4 and concentrated, and the product was purified by PTLC (3%
MeOH in CH2Cl2) to yield 3.0 mg of natural sarcodictyin A (7) (ca.
75% yield from 29, ca. 51% overall yield from 24) or 2.6 mg
sarcodictyin B (8) (ca. 75% yield from 30, ca. 44% overall yield from
24).
Reaction of Resin 25 with trans-Cinnamoyl Chloride. Toward
the Synthesis of Cinnamoate Ester 31. To a suspension of resin 25
(600 mg, 0.077 mmol) in DMF (5.0 mL) were added cinnamoyl chloride
(128 mg, 0.77 mmol, 10 equiv), Et3N (0.215 mL, 1.54 mmol, 20 equiv),
and 4-DMAP (46.5 mg, 0.385 mmol, 5.0 equiv), and the reaction
mixture was heated at 50 °C for 12 h. The resin was then filtered,
washed with CH2Cl2 containing 1% Et3N (5 × 20 mL), and Et2O (2 ×
100 mL), and then dried under high vacuum(>95% estimated yield).
DCC-Mediated Esterification of Resin 25 with Thiazole Acid Side
Chain Ar-II. Toward the Synthesis of Thiazole Ester 31. To a
suspension of resin 25 (200 mg, 0.026 mmol) in DMF (3.0 mL) was
added thiazole acid side chain Ar-II (Schemes 5 and 6) (48 mg, 0.26
General Procedure for the DCC/4-DMAP-Mediated Formation
of Ester or Amide Sarcodictyin Analogues 36. To a suspension of
resin 35 (1.0 equiv) in DMF were added DCC (10 equiv), 4-DMAP
(5.0 equiv), and an alcohol or an amine (10 equiv, amines were used
as HCl or PPTS salts), and the reaction mixture was allowed to react
for 20 h at ambient temperature. The resin was then filtered, washed
with CH2Cl2, MeOH, and Et2O, and dried under high vacuum (>85%
estimated yield).
General Procedure for the Ph3P/DEAD-Mediated Formation of
Ester Sarcodictyin Analogues 36. A suspension of resin 35 (1.0 equiv)
in THF containing Ph3P (10 equiv) and an alcohol (10 equiv) was cooled
to 0 °C. DEAD (10 equiv) was then added dropwise, and the reaction
mixture was allowed to warm to 25 °C. After 12 h, the resin was filtered,
washed with CH2Cl2 and Et2O, and dried under high vacuum (>90%
estimated yield).
General Procedure for the Formation of Azides 38 via a
Mitsunobu Reaction. A suspension of resin 31 (1.0 equiv) in THF
containing Ph3P (10 equiv) and (PhO)2P(O)N3 (10 equiv) was cooled
to 0 °C and treated with DEAD (10 equiv, dropwise addition). After
completion of the addition, the reaction mixture was allowed to warm
to 25 °C. After 4 h, the resin was filtered, washed with CH2Cl2
(containing 1% Et3N) and Et2O, and dried under high vacuum (>95%
yield based on NMR analysis of crude product, see compound 56 in
Supporting Information for spectroscopic data).

10824 J. Am. Chem. Soc., Vol. 120, No. 42, 1998
Nicolaou et al.
General Procedure for the Ph3P/H2O-Mediated Reduction of
Azides 38. Toward the Syntheses of Amides 39. A suspension of
resin 38 (1.0 equiv) in THF containing Ph3P (10 equiv) and H2O (50
equiv) was heated to 50 °C and stirred at that temperature for 8 h. The
resin was then filtered, washed with CH2Cl2 containing 1% Et3N and
Et2O, and dried under high vacuum (>95% estimated yield).
General Procedure for the Synthesis of Amides 39. A suspension
of the resin-bound amines (1.0 equiv) in CH2Cl2 at 25 °C was treated
with Et3N (15 equiv) and acetic anhydride (10 equiv) or benzoyl
chloride (10 equiv) for 10 h at ambient temperature. The resin was
then filtered, washed with CH2Cl2 containing 1% Et3N, and Et2O, and
dried under high vacuum (>90% estimated yield).
General Procedure for the Cleavage with PPTS/ROH. Synthesis
of Sarcodictyin Analogues 33 and 40. A suspension of resins 32 or
39 (1.0 equiv) in ROH at 25 °C was treated with PPTS (3.0 equiv).
After 15 h, the reaction was quenched with solid NaHCO3 (10 equiv),
filtered, and washed with CH2Cl2 and MeOH. The combined filtrates
were concentrated, and the product was purified by PTLC (60-90%,
see individual compounds in Supporting Information for exact overall
yields).
The so obtained methyl ester (0.50 g, 2.73 mmol, 1.0 equiv) was
saponified by the action of LiOH‚H2O (0.33 g, 8.19 mmol, 3.0 equiv)
in THF:H2O (1:1, 7 mL) as described for pyridine acid Ar-I above, to
produce thiazole acid Ar-II (0.46 g, 100% yield) as a white crystaline
solid. Rf ) 0.32 (silica gel, EtOAc); mp 172-173 °C (EtOAc); FT-IR
1
(neat) νmax 3413, 2919, 1690, 1672, 1625, 1496 cm-1; H NMR (500
MHz, CD3OD) δ 7.47 (s, 1 H), 7.40 (d, J ) 15.5 Hz, 1 H), 6.43 (d, J
) 15.5 Hz, 1 H), 2.55 (s, 3 H); 13C NMR (125 MHz, CD3OD) δ 170.4,
169.3, 152.4, 137.8, 123.5, 121.3, 18.9; HRMS (FAB) calcd for C7H7-
NO2S (MH+): 170.0276, found 170.0270.
Preparation of Oxazole Carboxylic Acid Ar-III. According to the
procedure described for the synthesis of pyridine derivative Ar-I above,
the corresponding oxazole aldehyde (0.7 g, 6.3 mmol, 1.0 equiv) was
reacted with Ph3PCHCO2Me (3.16 g, 9.45 mmol, 1.5 equiv) in benzene
(13 mL) to yield, after chromatographic purification (silica gel, EtOAc),
the expected R,â-unsaturated oxazole methyl ester (2.7 g, 96%) yield.
Rf ) 0.61 (silica gel, EtOAc); FT-IR (neat) νmax 3132, 3088, 1716,
1646, 1439, 1388 cm-1; 1H NMR (400 MHz, CDCl3) δ 7.58 (s, 1 H),
7.32 (d, J ) 15.5 Hz, 1 H), 6.44 (d, J ) 15.5 Hz, 1 H), 3.61 (s, 3 H),
2.35 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 167.0, 162.2, 138.9,
132.3, 118.8, 51.3, 13.4; HRMS (FAB) calcd for C8H9NO3 (MH+):
168.0661, found 168.0668.
General Procedure for the Cleavage with CSA/H2O. Synthesis
of Sarcodictyin Analogues 37. A suspension of resins 29 or 30 (1.0
equiv) in CH2Cl2/H2O (2:1) at 25 °C was treated with CSA (3.0 equiv).
After 40 h, the reaction was quenched with solid NaHCO3 (10 equiv),
filtered, and washed with CH2Cl2. The organic layer of the combined
filtrates was collected, dried over MgSO4, and concentrated, and the
product was purified by PTLC (60-90%, see individual compounds
in Supporting Information for exact overall yields).
The so obtained methyl ester (0.3 g, 1.80 mmol, 1.0 equiv) was
saponified by the action of LiOH‚H2O (0.22 g, 5.4 mmol, 3.0 equiv)
in THF:H2O (1:1, 15 mL) as described for pyridine carboxylic acid
Ar-I, to produce thiazole carboxylic acid Ar-III (0.28 g, 100%) in
quantitative yield as a white crystaline solid. Rf ) 0.33 (silica gel,
EtOAc); mp 165-166 °C (EtOAc); FT-IR (neat) νmax 3085, 2938, 2546,
1
1668, 1636, 1598, 1566, 1429 cm-1; H NMR (500 MHz, CD3OD) δ
General Procedure for the Transketalization with CSA/ ROH.
Synthesis of Sarcodictyin Analogues 37. A suspension of resins 36
in ROH (0.5 mL) at 25 °C was treated with CSA (3.0 equiv). After 15
h, the resin was quenched with NaHCO3 (10 equiv), filtered, and washed
with CH2Cl2 and MeOH. The combined filtrates were concentrated,
and the products were purified by PTLC (60-90%, see individual
compounds in Supporting Information for exact overall yields).
Preparation of Pyridine Carboxylic Acid Ar-I. To a solution of
2-pyridinecarboxaldehyde (2.0 g, 18.7 mmol, 1.0 equiv) in benzene
(37 mL) was added Ph3PCHCO2Me (9.36 g, 28.0 mmol, 1.5 equiv),
and the reaction mixture was heated at reflux temperature for 2 h. After
the end of the reaction was established (TLC), the solvent was
evaporated under reduced pressure, and the crude product was purified
by flash column chromatography (silica gel, Et2O-hexanes, 1:1, Rf )
0.26) furnishing the expected R,â-unsaturated methyl ester (2.9 g, 95%
yield). The so prepared methyl ester (1.5 g, 9.2 mmol, 1.0 equiv) was
treated in THF:H2O (1:1, 30 mL) with LiOH‚H2O (1.16 g, 27.6 mmol,
3.0 equiv) at ambient temperature for 3 h after which time the end of
the reaction was established (TLC). The reaction mixture was extracted
with saturated aqueous NaHCO3 (3 × 20 mL), and the combined
aqueous extracts were acidified with 1 M HCl to pH 4 and further
extracted with EtOAc (4 × 20 mL). Concentration of the combined
organic solutions furnished, in quantitative yield, essentially pure
carboxylic acid Ar-I (1.4 g, 100% yield). Rf ) 0.35 (silica gel, EtOAc);
mp 141-142 °C (EtOAc); FT-IR (neat) νmax 3434, 3091, 1700, 1644,
1595, 1568, 1464 cm-1; 1H NMR (500 MHz, CD3OD) δ 8.34 (d, J )
5.0 Hz, 1 H), 7.65 (dt, J ) 8.0, 1.5 Hz, 1 H), 7.43 (d, J ) 8.0 Hz, 1
H), 7.35 (d, J ) 16.0 Hz, 1 H), 7.17 (m, 1 H), 6.63 (d, J ) 16.0 Hz,
1 H); 13C NMR (125 MHz, CD3OD) δ 170.5, 154.5, 150.8, 143.6, 138.9,
125.7, 125.2, 125.2; HRMS (FAB) calcd for C8H7NO2 (MH+):
150.0555, found 150.0551.
7.90 (s, 1 H), 7.35 (d, J ) 15.5 Hz, 1 H), 6.34 (d, J ) 15.5 Hz, 1 H),
2.34 (s, 3 H); 13C NMR (125 MHz, CD3OD) δ 169.9, 164.7, 141.6,
138.2, 133.9, 120.6, 13.5; HRMS (FAB) calcd for C7H7NO3 (MH+):
154.0504, found 154.0508.
Attachment of the Pyridine Side Chain and Desilylation. Syn-
thesis of Compound 42. To a solution of hydroxy compound 41 (23.0
mg, 0.046 mmol, 1.0 equiv) in CH2Cl2 (2.2 mL) were added 4-DMAP
(2.8 mg, 0.023 mmol, 0.5 equiv), pyridine carboxylic acid Ar-I (10.2
mg, 0.068 mmol, 1.5 equiv), and DCC (18.8 mg, 0.091 mmol, 2.0
equiv) at 25 °C. The reaction mixture was stirred for 20 h at that
temperature and then concentrated. The crude mixture was purified by
flash chromatography (silica gel, EtOAc-hexane, 1:4, Rf ) 0.28) to
furnish the corresponding ester (24.5 mg, 85%). The latter compound
was desilylated as follows: A solution of the silyl ether (24.5 mg, 0.038
mmol, 1.0 equiv) in THF (1 mL) was treated with TBAF (1.0 M in
THF, 77 µL, 2.0 equiv), and the reaction mixture was stirred for 1 h at
25 °C. The solvent was removed under reduced pressure, and the crude
product was purified by flash chromatography (silica gel, EtOAc-
hexane, 1:1) to yield alcohol 42 (16.1 mg, 87%). Rf ) 0.10 (silica gel,
EtOAc-hexane, 1:1); [R]25 -13.8 (c ) 0.8, CHCl3); FT-IR (neat)
D
1
νmax 3410, 2961, 1713, 1647, 1583, 1468, 1434 cm-1; H NMR (600
MHz, CDCl3) δ 8.64 (d, J ) 5.5 Hz, 1 H), 7.72 (dt, J ) 9.0, 2.0 Hz,
1 H), 7.67 (d, J ) 15.5 Hz, 1 H), 7.43 (d, J ) 7.5 Hz, 1 H), 7.28 (dd,
J ) 9.0, 5.5 Hz, 1 H), 6.95 (d, J ) 15.5 Hz, 1 H), 6.24 (d, J ) 7.5 Hz,
1 H), 6.05 (d, J ) 7.5 Hz, 1 H), 5.50 (d, J ) 11.5 Hz, 1 H), 5.27 (bs,
1 H), 4.83 (d, J ) 8.5 Hz, 1 H), 4.17 (d, J ) 14.0 Hz, 1 H), 3.97-3.87
(m, 1 H), 3.75-3.69 (m, 2 H), 3.24 (s, 3 H), 2.65-2.57 (m, 1 H),
2.36-2.28 (m, 1 H), 2.03-1.95 (m, 1 H), 1.63-1.47 (m, 4 H), 1.51
(s, 3 H), 1.47 (s, 3 H), 1.00 (d, J ) 7.5 Hz, 3 H), 0.92 (d, J ) 7.5 Hz,
3 H); 13C NMR (150 MHz, CDCl3) δ 165.8, 150.1, 136.9, 136.8, 135.4,
135.1, 133.8, 129.4, 124.5, 122.3, 121.5, 117.1, 90.2, 82.1, 67.9, 67.3,
49.6, 42.0, 38.7, 33.9, 31.5, 28.9, 25.6, 23.9, 22.2, 21.0; HRMS (FAB)
calcd for C29H37NO5 (M + Na+): 502.2569, found 502.2556.
Attachment of the Thiazole Side Chain and Desilylation. Syn-
thesis of Compound 43. According to the procedure described above
for compound 42, to a solution of hydroxy compound 41 (15 mg, 0.030
mmol, 1.0 equiv) in CH2Cl2 (1.8 mL) were added 4-DMAP (1.8 mg,
0.015 mmol, 0.5 equiv), thiazole carboxylic acid Ar-II (6.5 mg, 0.039
mmol, 1.3 equiv), and DCC (11.3 mg, 0.055 mmol, 1.7 equiv) at 25
°C to provide, after flash chromatography (silica gel, EtOAc-hexane,
1:4), the corresponding ester (12 mg, 61% yield). Desilylation of the
latter compound (6.0 mg, 9.1 mmol, 1.0 equiv) in THF (1 mL) with
Preparation of Thiazole Carboxylic Acid Ar-II. According to the
procedure described for the synthesis of pyridine derivative Ar-I, the
corresponding thiazole aldehyde (2.0 g, 16 mmol, 1.0 equiv) was reacted
with Ph3PCHCO2Me (8.0 g, 24.0 mmol, 1.5 equiv) in benzene (32 mL)
to yield after chromatographic purification (silica gel, Et2O-hexanes,
3:1), the expected R,â-unsaturated thiazole methyl ester (2.8 g, 97%
yield). Rf ) 0.42 (silica gel, Et2O-hexanes, 3:1); FT-IR (neat) νmax
3095, 3048, 1707, 1631, 1431, 1300 cm-1; 1H NMR (500 MHz, CDCl3)
δ 7.54 (d, J ) 15.5 Hz, 1 H), 7.26 (s, 1H), 6.70 (d, J ) 15.5 Hz, 1 H),
3.77 (s, 3 H), 2.71 (s, 3 H); 13C NMR (125 MHz, CDCl3) δ 167.6,
166.8, 151.3, 136.4, 121.5, 119.8, 51.6, 19.3; HRMS (FAB) calcd for
C8H9NO2S (MH+): 184.0432, found 184.0437.

Combinatorial Sarcodictyin Libraries
J. Am. Chem. Soc., Vol. 120, No. 42, 1998 10825
TBAF (1.0 M in THF, 18 µL, 2.0 equiv) furnished after flash
chromatography (silica gel, EtOAc-hexane, 1:2) alcohol 43 (5.5 mg,
100%). Rf ) 0.18 (silica gel, EtOAc-hexane, 1:2); [R]25D +19.6 (c )
The so obtained aldehyde 45 (7.0 mg, 0.015 mmol, 1.0 equiv) was
treated with 2-methyl-2-butene (2.0 M in THF, 1.5 mL), NaH2PO4 (5.3
mg, 0.044 mmol, ca. 3 equiv), and NaClO2 (8.0 mg, 0.088 mmol, ca.
6 equiv) in THF:tBuOH:H2O (5:5:1, 2.2 mL) at 0 °C. The reaction
mixture was stirred at 0 °C for 2 h after which time a solution of CH2N2
in Et2O (excess) was added and stirring was continued for an additional
10 min at 25 °C. The excess CH2N2 was removed by a stream of argon,
and the reaction mixture was extracted with Et2O (3 × 8 mL), dried
over Na2SO4, and concentrated. The crude residue was purified by flash
chromatography (silica gel, EtOAc-hexane, 1:4) to afford sarcodictyin
0.55, CHCl3); FT-IR (neat) νmax 3414, 2961, 1711, 1636, 1450 cm-1
;
1H NMR (600 MHz, CDCl3) δ 7.54 (d, J ) 15.5 Hz, 1 H), 7.29 (s, 1
H), 6.73 (d, J ) 15.5 Hz, 1 H), 6.21 (d, J ) 6.0 Hz, 1 H), 6.04 (d, J
) 6.0 Hz, 1 H), 5.55 (d, J ) 9.5 Hz, 1 H), 5.27 (bs, 1 H), 4.82 (d, J
) 7.5 Hz, 1 H), 4.15 (d, J ) 12.0 Hz, 1 H), 3.95-3.88 (m,2 H), 3.23
(s, 3 H), 2.72 (s, 3 H), 2.62-2.54 (m, 2 H), 2.32 (m, 1 H), 1.99 (m, 1
H), 1.59-1.55 (m, 2 H), 1.50 (s, 3 H), 1.45 (s, 3 H), 1.44-1.35 (m, 1
H), 1.30-1.25 (m, 1 H), 0.97 (d, J ) 6.5 Hz, 3 H), 0.92 (d, J ) 6.5
Hz, 3 H); 13C NMR (150 MHz, CDCl3) δ 167.1, 166.3, 151.3, 136.8,
136.7, 135.5, 135.1, 133.9, 129.4, 121.8, 121.5, 120.2, 117.1, 90.2,
81.9, 67.3, 49.6, 42.1, 38.7, 33.9, 28.0, 26.0, 24.3, 23.9, 22.2, 22.1,
20.5, 19.4; HRMS (FAB) calcd for C28H37NO5S (M + Cs+): 632.1447,
found 632.1469.
analogue 48 (3.2 mg, 43% for two steps). Rf ) 0.56 (silica gel, EtOAc-
1
hexane, 1:1); [R]25 -37.14 (c ) 0.07, CHCl3); H NMR (600 MHz,
D
CDCl3) δ 8.66 (d, J ) 4.0 Hz, 1 H), 7.76 (m, 1 H), 7.69 (d, J ) 16.0
Hz, 1 H), 7.43 (d, J ) 11.0 Hz, 1 H), 7.31 (m, 1 H), 7.05 (d, J ) 16.0
Hz, 1 H), 6.80 (d, J ) 10.0 Hz, 1 H), 6.51 (d, J ) 5.5 Hz, 1 H), 6.22
(d, J ) 5.5 Hz, 1 H), 5.30 (bs, 1 H), 4.82 (d, J ) 7.5 Hz, 1 H), 4.15-
4.08 (m, 1 H), 3.71 (s, 3 H), 3.24 (s, 3 H), 2.70-2.65 (m, 1 H), 2.42-
2.36 (m, 1 H), 2.15-1.97 (m, 1 H), 1.70-1.46 (m, 4 H), 1.52 (s, 3 H),
Attachment of the Oxazole Side Chain and Desilylation. Synthesis
of Compound 44. According to the procedure described for the
synthesis of compound 42, alcohol 41 (21 mg, 0.042 mmol, 1.0 equiv)
was treated with 4-DMAP (2.5 mg, 0.020 mmol, 0.5 equiv), oxazole
carboxylic acid Ar-III (8.4 mg, 0.055 mmol, 1.3 equiv), and DCC (16.9
mg, 0.082 mmol, 2.0 equiv) in CH2Cl2 (2 mL) to produce, after
chromatographic purification (silica gel, EtOAc-hexane, 1:4, Rf )
0.43), the desired ester (23 mg, 86%). The latter compound (23 mg,
0.036 mmol, 1.0 equiv) was deprotected by the action of TBAF (1.0
M in THF, 72 µL, 2.0 equiv) according to the procedure described
above for compound 42 to afford, after chromatographic purification
(flash column, silica gel, EtOAc-hexane, 1:1), alcohol 44 (16 mg,
1.37 (s, 3 H), 0.98 (d, J ) 6.5 Hz, 3 H), 0.93 (d, J ) 6.5 Hz, 3 H); 13
C
NMR (150 MHz, CDCl3) δ 165.8, 152.6, 150.1, 137.2, 137.0, 136.8,
136.6, 135.4, 135.1, 133.8, 129.4, 124.5, 122.3, 121.5, 117.1, 90.2,
82.1, 68.0, 67.3, 49.6, 42.0, 38.7, 33.9, 31.5, 29.0, 25.6, 24.3, 23.9,
22.2, 20.5; HRMS (FAB) calcd for C30H37NO6 (MH+): 508.2699, found
508.2681.
Preparation of Sarcodictyin Analogue 49 via Aldehyde 46.
According to the procedure described above for the synthesis of
compound 47, to a solution of alcohol 43 (5.0 mg, 0.010 mmol, 1.0
equiv) in CH2Cl2 (1.0 mL) were added NaHCO3 (6.7 mg, 0.080 mmol,
8.0 equiv) and Dess-Martin periodinane (8.5 mg, 0.02 mmol, 2.0
equiv), and the reaction mixture was stirred for 30 min at 25 °C to
afford after flash chromatography (silica gel, EtOAc-hexane, 1:4; Rf
) 0.45) the corresponding aldehyde 46 (2.0 mg, 40%) which was used
directly in the next step. Thus, aldehyde 46 (2.0 mg, 0.004 mmol, 1.0
equiv) in tBuOH:H2O (5:1, 0.6 mL) was treated with 2-methyl-2-butene
(2.0 M in THF, 0.5 mL, 1.0 mmol), NaH2PO4 (1.4 mg, 0.012 mmol,
3.0 equiv), and NaClO2 (2.2 mg, 0.024 mmol, 6.0 equiv) at 0 °C. The
reaction mixture was stirred at 0 °C for 2 h after which time a solution
of CH2N2 (excess) in Et2O was added, and stirring was continued for
an additional 10 min at 25 °C. The excess CH2N2 was removed by a
stream of argon, and the reaction mixture was extracted with Et2O (3
× 5 mL), dried over Na2SO4, and concentrated. The crude residue was
purified by flash chromatography (silica gel, EtOAc-hexane, 1:4) to
yield sarcodictyin analogue 49 (1.5 mg, 71% for 2 steps). Rf ) 0.45
(silica gel, EtOAc-hexane, 1:4); [R]25D -13.4 (c ) 0.10, CHCl3); FT-
92%). Rf ) 0.21 (silica gel, EtOAc-hexane, 1:1); [R]25 +8.1 (c )
D
1.6, CHCl3); FT-IR (neat) νmax 3410, 2961, 2865, 1712, 1651, 1451
1
cm-1; H NMR (600 MHz, CDCl3) δ 7.68 (s, 1 H), 7.44 (d, J ) 15.5
Hz, 1 H), 6.59 (d, J ) 15.5 Hz, 1 H), 6.19 (d, J ) 6.0 Hz, 1 H), 6.03
(d, J ) 6.0 Hz, 1 H), 5.54 (d, J ) 9.5 Hz, 1 H), 5.25 (bs, 1 H), 4.78
(d, J ) 7.5 Hz, 1 H), 4.14 (d, J ) 12.0 Hz, 1 H), 3.93-3.87 (m, 2 H),
3.22 (s, 3 H), 2.65 (bd, J ) 7.5 Hz, 1 H), 2.58 (m, 1 H), 2.47 (s, 3 H),
2.30 (m, 1 H), 1.98 (m, 1 H), 1.59-1.51 (m, 2 H), 1.49 (s, 3 H), 1.43
(s, 3 H), 1.40-1.34 (m, 1 H), 1.28-1.27 (m, 1 H), 0.96 (d, J ) 6.5
Hz, 3 H), 0.90 (d, J ) 6.5 Hz, 3 H); 13C NMR (150 MHz, CDCl3) δ
165.9, 162.6, 139.2, 137.1, 136.7, 135.4, 135.1, 133.9, 132.7, 129.3,
121.5, 119.5, 117.1, 90.2, 81.9, 67.3, 49.6, 42.0, 38.6, 33.8, 31.4, 28.9,
24.3, 23.8, 22.2, 22.1, 20.5, 13.9; HRMS (FAB) calcd for C28H37NO6
(M + Na+): 506.2519, found 506.2502.
Oxidation of Alcohol 44. Synthesis of Aldehyde 47. To a solution
of alcohol 44 (16 mg, 0.033 mmol, 1.0 equiv) in CH2Cl2 (2.0 mL)
were added NaHCO3 (20 mg, 0.238 mmol, ca. 7 equiv) and Dess-
Martin periodinane (25 mg, 0.060 mmol, ca. 2 equiv) in CH2Cl2 (1.5
mL), and the reaction mixture was stirred for 50 min at 25 °C after
which time 2-propanol (excess) was added followed by EtOAc (2.0
mL). The precipitates were filtered off through a short plug of silica,
and the filtrates were concentrated and purified by flash chromatography
(silica gel, EtOAc-hexane, 1:1) to yield the desired aldehyde 47 (13.3
mg, 84%). Rf ) 0.56 (silica gel, EtOAc-hexane, 1:1); [R]25D +85.0 (c
IR (neat) νmax 2960, 2360, 2337, 1714, 1636, 1436, 1268, 1157 cm-1
;
1H NMR (600 MHz, CDCl3) δ 7.54 (d, J ) 15.5 Hz, 1 H), 7.29 (s, 1
H), 6.73 (d, J ) 15.5 Hz, 1 H), 6.73 (d, J ) 10.0 Hz, 1 H), 6.50 (d, J
) 6.0 Hz, 1 H), 6.17 (d, J ) 6.0 Hz, 1 H), 5.29 (bs, 1 H), 4.80 (d, J
) 7.5 Hz, 1 H), 4.14 (m, 1 H), 3.70 (s, 3 H), 3.23 (s, 3 H), 2.72 (s, 3
H), 2.70-2.64 (m, 1 H), 2.38 (m, 1 H), 2.04 (m, 1 H), 1.63-1.55 (m,
2 H), 1.51 (s, 3 H), 1.45 (s, 3 H), 1.36-1.28 (m, 1 H), 1.26-1.11 (m,
1 H), 0.98 (d, J ) 6.5 Hz, 3 H), 0.93 (d, J ) 6.5 Hz, 3 H); 13C NMR
(150 MHz, CDCl3) δ 167.1, 166.4, 154.9, 151.3, 146.4, 136.7, 134.8,
133.9, 132.0, 131.2, 121.9, 121.5, 120.1, 115.6, 100.8, 89.5, 81.8, 51.9,
50.2, 41.7, 38.8, 34.7, 31.5, 28.9, 24.4, 22.2, 22.0, 20.5, 19.4; HRMS
(FAB) calcd for C29H37NO6S (M + Cs+): 660.1396, found 660.1416.
) 1.3, CHCl3); FT-IR (neat) νmax 2962, 1697, 1650, 1450, 1301 cm-1
;
1H NMR (600 MHz, CDCl3) δ 9.27 (s, 1 H), 7.69 (s, 1 H), 7.44 (d, J
) 15.5 Hz, 1 H), 6.59 (d, J ) 15.5 Hz, 1 H), 6.47 (d, J ) 10.0 Hz, 1
H), 6.30 (d, J ) 6.0 Hz, 1 H), 6.15 (d, J ) 6.0 Hz, 1 H), 5.32 (bs, 1
H), 4.77 (d, J ) 7.5 Hz, 1 H), 3.27 (m, 1 H), 3.24 (s, 3 H), 2.75 (m,
1 H), 2.47 (s, 3 H), 2.39 (m, 1 H), 2.10 (m, 1 H), 1.65-1.61 (m, 2 H),
1.52 (s, 3 H), 1.44 (s, 3 H), 1.38-1.35 (m, 1 H), 1.25-1.19 (m, 1 H),
0.99 (d, J ) 6.5 Hz, 3 H), 0.94 (d, J ) 6.5 Hz, 3 H); 13C NMR (150
MHz, CDCl3) δ 193.9, 166.0, 162.7, 159.4, 142.0, 139.3, 137.0, 135.4,
133.9, 132.9, 129.8, 121.5, 119.4, 114.6, 89.3, 81.6, 50.3, 41.3, 39.0,
35.6, 31.5, 28.9, 24.3, 24.2, 22.1, 22.0, 20.5, 13.9; HRMS (FAB) calcd
for C28H35NO6 (M + Na+): 504.2362, found 504.2345.
Preparation of Sarcodictyin Analogue 50. According to the
procedure described above for the synthesis of compound 49, aldehyde
47 (8.5 mg, 0.017 mmol, 1.0 equiv) was treated with 2-methyl-2-butene
(2.0 M in THF, 1.0 mL), NaH2PO4 (6.3 mg, 0.053 mmol, ca. 3 equiv),
t
and NaClO2 (9.6 mg, 0.106 mmol, ca. 6 equiv) in BuOH:H2O (5:1,
1.2 mL) to furnish, after diazoethane treatment and chromatographic
purification (silica gel, EtOAc-hexane, 1:2), sarcodictyin analogue 50
(8.0 mg, 87% for two steps). Rf ) 0.35 (silica gel, EtOAc-hexane,
1:2); [R]25D +3.6 (c ) 0.8, CHCl3); FT-IR (neat) νmax 2963, 1713, 1650,
Preparation of Sarcodictyin Analogue 48 via Aldehyde 45.
According to the procedure described above for the synthesis of
compound 47, alcohol 42 (16.0 mg, 0.033 mmol, 1.0 equiv) was treated
with NaHCO3 (26.6 mg, 0.334 mmol, ca. 10 equiv) and Dess-Martin
periodinane (35.4 mg, 0.083 mmol, ca. 2.5 equiv) in CH2Cl2 (1.5 mL)
to produce, after chromatographic purification (silica gel, EtOAc-
hexane, 1:4, Rf ) 0.35), the corresponding aldehyde (7.0 mg, 44%).
1
1449, 1301 cm-1; H NMR (600 MHz, CDCl3) δ 7.68 (s, 1 H), 7.44
(d, J ) 15.5 Hz, 1 H), 6.72 (d, J ) 10.0 Hz, 1 H), 6.60 (d, J ) 15.5
Hz, 1 H), 6.50 (d, J ) 6.0 Hz, 1 H), 6.14 (d, J ) 6.0 Hz, 1 H), 5.29
(bs, 1 H), 4.78 (d, J ) 7.5 Hz, 1 H), 4.18-4.10 (m, 3 H), 3.22 (s, 3
H), 2.66 (m, 1 H), 2.47 (s, 3 H), 2.39 (m, 1 H), 2.03 (m, 1 H), 1.63-
1.57 (m, 2 H), 1.51 (s, 3 H), 1.44 (s, 3 H), 1.34-1.31 (m, 2 H), 1.26

10826 J. Am. Chem. Soc., Vol. 120, No. 42, 1998
Nicolaou et al.
(t, J ) 7.0 Hz, 3 H), 0.97 (d, J ) 6.5 Hz, 3 H), 0.92 (d, J ) 6.5 Hz,
3 H); 13C NMR (150 MHz, CDCl3) δ 166.8, 166.0, 162.6, 146.1, 139.2,
137.1, 134.6, 133.8, 132.7, 132.3, 131.3, 121.5, 119.5, 115.6, 89.4,
81.8, 60.6, 50.2, 41.7, 38.8, 34.7, 31.5, 28.9, 24.3, 22.2, 22.0, 20.5,
14.1, 13.9; HRMS (FAB) calcd for C30H39NO7 (M + Cs+): 658.1781,
found 658.1762.
ambient temperature there was added a catalytic amount of CSA (10%
mol), and stirring was continued for 72 h. After completion of the
reaction was established by TLC (40 h), quenching with solid NaHCO3
,
filtration, and chromatographic purification (silica gel, EtOAc) afforded
sarcodictyin analogue 54 (5.1 mg, 95% yield). Rf ) 0.37 (silica gel,
EtOAc); [R]25D -28.9 (c ) 0.35, CHCl3); FT-IR (neat) νmax 3348, 2962,
1
1737, 1704, 1638, 1233, 1155 cm-1; H NMR (600 MHz, CDCl3) δ
Preparation of Sarcodictyin Analogue 52. A solution of alcohol
51 (2.5 mg, 0.0052 mmol, 1.0 equiv) in CH2Cl2 (1.0 mL) at -78 °C
was treated with DAST [(diethylamino)sulfur trifluoride] (1.3 µL, 0.010
mmol, ca. 2 equiv) and stirred at that temperature for 3 h. The reaction
mixture was quenched by the addition of solid NaHCO3 (30 mg),
warmed to 25 °C, concentrated, and purified by flash chromatography
(silica gel, EtOAc:CH2Cl2:MeOH, 10:10:1) to afford the desired
sarcodictyin analog 52 (2.5 mg, 99% yield). Rf ) 0.31 (silica gel,
EtOAc:CH2Cl2:MeOH, 10:10:1); [R]25D - 32.4 (c ) 0.25, CHCl3); FT-
IR (neat) νmax 2961, 1762, 1637, 1451, 1384 cm-1; 1H NMR (600 MHz,
CDCl3) δ 7.52 (d, J ) 15.5 Hz, 1 H), 7.44 (s, 1 H), 7.08 (s, 1 H), 6.56
(d, J ) 15.5 Hz, 1 H), 6.14 (d, J ) 6.0 Hz, 1 H), 5.97 (dd, J ) 6.0, 3.0
Hz, 1 H), 5.67 (dd, J ) 9.5, 5.0 Hz, 1 H), 5.26 (bs, 1 H), 5.02 (dd, J
) 49.0, 10.0 Hz, 1 H), 4.80 (d, J ) 7.5 Hz, 1 H), 4.62 (dd, J ) 48.0,
10.0 Hz, 1 H), 3.98-3.93 (m, 1 H), 3.69 (s, 3 H), 3.22 (s, 3 H), 2.62
(m, 1 H), 2.29 (m, 1 H), 1.99 (m, 1 H), 1.64-1.55 (m, 2 H), 1.52 (s,
3 H), 1.44 (s, 3 H), 1.23-1.20 (m, 2 H), 0.96 (d, J ) 6.5 Hz, 3 H),
0.91 (d, J ) 6.5 Hz, 3 H); 13C NMR (150 MHz, CDCl3) δ 166.7, 139.2,
138.9, 138.8, 138.4, 136.4, 134.4, 134.3, 130.6, 122.7, 121.2, 116.0,
115.6, 90.1, 87.4, 81.5, 49.8, 42.2, 38.7, 34.1, 33.6, 31.4, 29.0, 24.4,
24.2, 22.2, 22.1, 20.5; HRMS (FAB) calcd for C28H37N2O4F (M +
Cs+): 617.1792, found 617.1813.
7.51 (d, J ) 15.5 Hz, 1 H), 7.46 (s, 1 H), 7.08 (s, 1 H), 6.55 (d, J )
15.5 Hz, 1 H), 6.14 (d, J ) 6.0 Hz, 1 H), 6.11 (d, J ) 6.0 Hz, 1 H),
5.58 (d, J ) 9.5 Hz, 1 H), 5.26 (bs, 1 H), 4.79 (d, J ) 7.5 Hz, 1 H),
4.59 (s, 2 H), 3.98 (m, 1 H), 3.70 (s, 3 H), 3.25 (bs, 1 H), 2.60 (m, 1
H), 2.29 (m, 1 H), 2.04 (s, 3 H), 2.00 (m, 1 H), 1.68-1.53 (m, 2 H),
1.51 (s, 3 H), 1.46 (s, 3 H), 1.41-1.33 (m, 1 H), 1.25-1.22 (m, 1 H),
0.97 (d, J ) 6.5 Hz, 3 H), 0.91 (d, J ) 6.5 Hz, 3 H); 13C NMR (125
MHz, CDCl3) δ 170.8, 166.7, 139.2, 138.3, 136.9, 136.3, 134.2, 133.9,
133.4, 131.7, 122.7, 121.2, 115.9, 112.2, 90.4, 81.2, 67.4, 42.3, 38.7,
34.2, 33.7, 31.6, 29.1, 25.8, 24.4, 22.2, 22.1, 21.2, 20.6; HRMS (FAB)
calcd for C29H38N2O6 (M + Cs+): 643.1784, found 643.1763.
Conclusion
In this article, we described the development of solid phase
chemistry for the chemical synthesis of the naturally occurring
sarcodictyins A (7) and B (8) and its application to the
construction of a sarcodictyin combinatorial library. This library
was complemented with compounds synthesized by solution
methods and was subjected to biological evaluation with regards
to tubulin polymerization and cytotoxicity. The results were
useful both in terms of new synthetic methodology development
and structure-activity relationships in this new structural class
of compounds. Furthermore, the chemistry described herein
demonstrates the use of REC chemistry19 in chemical biology
studies and sets the stage for further developments in the field
of cancer chemotherapy.
Preparation of Sarcodictyin Analogue 53. To a solution of alcohol
41 (5.0 mg, 0.01 mmol, 1.0 equiv) in CH2Cl2 (1.0 mL) there were
added acetic anhydride (5.0 mg, 0.052 mmol, 5.2 equiv), Et3N (10 µL,
0.07 mmol, 6.8 equiv), and 4-DMAP (2.0 mg, 0.016 mmol, 1.6 equiv),
and the reaction mixture was stirred at ambient temperature for 2 h.
After completion of the reaction was established (TLC), quenching with
saturated NaHCO3 solution (2 × 2 mL), removal of the solvents under
reduced pressure, and flash chromatographic purification (silica gel,
EtOAc) afforded sarcodictyin analogue 53 in quantitative yield (5.2
mg, 100%). Rf ) 0.41 (silica gel, EtOAc); [R]25 - 16.2 (c ) 0.55,
Acknowledgment. We thank Dr. D. H. Huang and Dr. G.
Siuzdak for NMR and mass spectroscopic assistance, respec-
tively. This work was supported by The Skaggs Institute for
Chemical Biology and the National Institutes of Health USA,
by fellowships from Novartis (to D.V.), and the Department of
Defense, USA (to J.P.), and grants from CaP CURE, Novartis,
Pfizer, Merck, DuPont Merck, Schering Plough, and Hoffmann-
LaRoche.
D
CHCl3); FT-IR (neat) νmax 2961, 1737, 1704, 1638, 1450, 1381 cm-1
;
1H NMR (600 MHz, CDCl3) δ 7.51 (d, J ) 15.5 Hz, 1 H), 7.45 (s, 1
H), 7.07 (s, 1 H), 6.55 (d, J ) 15.5 Hz, 1 H), 6.15 (d, J ) 6.0 Hz, 1
H), 6.01 (d, J ) 6.0 Hz, 1 H), 5.60 (d, J ) 9.5 Hz, 1 H), 5.26 (bs, 1
H), 4.79 (d, J ) 7.5 Hz, 1 H), 4.55 (d, J ) 12.5 Hz, 1 H), 4.51 (d, J
) 12.5 Hz, 1 H), 3.96 (m, 1 H), 3.69 (s, 3 H), 3.19 (s, 3 H), 2.59 (m,
1 H), 2.27 (m, 1 H), 2.02 (s, 3 H), 1.98 (m, 1 H), 1.61-1.53 (m, 2 H),
1.51 (s, 3 H), 1.43 (s, 3 H), 1.43-1.40 (m, 1 H), 1.24-1.21 (m, 1 H),
0.96 (d, J ) 6.5 Hz, 3 H), 0.91 (d, J ) 6.5 Hz, 3 H); 13C NMR (150
MHz, CDCl3) δ 170.7, 166.7, 139.2, 138.4, 136.8, 136.3, 134.7, 134.3,
132.8, 130.0, 122.7, 121.2, 116.0, 115.9, 90.2, 81.5, 67.0, 49.7, 42.3,
38.8, 34.1, 33.6, 31.5, 29.1, 24.5, 24.3, 22.2, 22.0, 21.2, 20.5; HRMS
(FAB) calcd for C30H40N2O6 (M + Cs+): 657.1941, found 657.1922.
Preparation of Sarcodictyin Analogue 54. To a stirring solution
of ketal 53 (5.2 mg, 0.01 mmol, 1.0 equiv) in CH2Cl2:H2O (10:1) at
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