relative to the literature (lit. 450 mg/L, 45% yield). After
extraction and purification, 155 mg/L of 2 was recovered
(lit. 110 mg/L).
Scheme 1. Eleven-Step Preparation of Squalamine, 12, from 1
The viability of the 10 chemical steps was demonstrated
successfully. The reduction of 24a to 312 was accomplished
in 71% yield using lithium in ammonia. This method is
commonly used to afford the trans AB-ring junction.7
Ketalization was performed utilizing ethylene glycol in
chlorotrimethylsilane in good yield.8 This reaction was
accomplished at 10% concentration of substrate, which
allows for efficient scale-up of this procedure. Selective
oxidation of the C-22 alcohol with bleach and TEMPO as
catalyst9 afforded 5 in 98% yield. Wadsworth-Emmons
reagent 610 was utilized to afford enone 7 efficiently (82%).
Steroid 7 was reduced stereoselectively as before with borane
and (R)-MeCBS11 to yield 8 in good yield. The diastereo-
meric excess was not evaluated at this stage, but was after
conversion to 11. The product 8 was isolated by recrystal-
lization and converted to 9 by hydrogenation. Deprotection
of the ketal afforded intermediate 10, which contains the C7,-
24-diol. The key step to this short route is the selective
sulfation of the C24-hydroxyl group in 10 to afford 11.
Selective sulfation was accomplished successfully with a very
small excess (5%) of sulfur trioxide-pyridine complex. The
diastereomeric excess in the sulfate 11 was calculated to be
95% based on the HPLC method, which is comparable to
what was achieved previously (94%).2 This suggests that the
stereoselectivity of the chiral reduction is not significantly
influenced by the protecting group on C-7.
The short 10-step route to squalamine 12 from the fungal
metabolite 2 has been accomplished. The overall method has
potential to improve the supply and cost of this promising
Phase II clinical candidate. Research activity must now be
directed at the biotransformation step in order to make this
potential manufacturing method a reality.
Acknowledgment. This research was supported by a
Small Business Innovation Research Grant (1 R43 CA
80473-01) from the National Cancer Institute. The authors
thank Hong-Seok Kim, Kyungpook National University,
Taegu, South Korea, for providing a reference sample of
compound 3.
synthesis of squalamine, because 11 has been previously used
as an intermediate to yield the natural product in two steps.2,6
The best preliminary result at adopting the fungal 7R-
hydroxylation of 1 with D. gossypina (ATCC 20576) is
described in detail in the Supporting Information. The yield
of 2 was estimated to be 800 mg/L at its peak concentration
during fermentation (26% yield), based on HPLC analysis.
This yield was obtained at a 3 g/L substrate concentration,
substantially higher than that described in the literature (1.0
g/L).4a Therefore, the yield per liter is slightly improved
Supporting Information Available: Experimental pro-
cedures and analytical data for compounds 2-11. This
material is available free of charge via the Internet at
OL0059495
(7) Starr, J. E. In Steroid Reactions; Djerassi, C., Ed.; Holden-Day,
Inc.: San Francisco, 1963; Chapter 7, pp 300-307.
(8) Chan, T. H.; Brook, M. A.; Chaly, T. Synthesis 1983, 203-205.
(9) A General Synthetic Method for the Oxidation of Primary Alcohols
to Aldehydes: (S)-(+)-2-Methylbutanal. Anelli, P. L.; Montanari, F.; Quici,
S. Org. Synth. 69, 212.
(10) Jones, S. R.; Selinsky, B. S.; Rao, M. N.; Zhang, X.; Kinney, W.
A.; Tham, F. S. J. Org. Chem. 1998, 63, 3786-3789.
(4) (a) Chemical and biological synthesis of 2 is described in: Despreaux,
C. W.; Rittweger, K. R.; Palleroni, N. J. Appl. EnViron. Microbiol. 1986,
51, 946-949. (b) Despreaux, C.; Narwid, T. A.; Palleroni, N. J.; Uskokovic,
M. R. U.S. Patent 4,230,625. (c) Despreaux, C.; Narwid, T. A.; Palleroni,
N. J.; Uskokovic, M. R. U.S. Patent 4,301,246.
(5) Moriarty, R. M.; Tuladhar, S. M.; Guo, L.; Wehrli, S. Tetrahedron
Lett. 1994, 35, 8103-8106.
(6) Weis, A. L.; Bakos, T.; Alferiev, I.; Zhang, X.; Shao, B.; Kinney,
W. A. Tetrahedron Lett. 1990, 40, 4863-4864.
(11) (a) (R)-MeCBS refers to the R-isomer of the reagent developed in
Corey etal. ( Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen, C.-P.; Singh,
V. K. J. Am. Chem. Soc. 1987, 109, 7925-7926) and prepared by Callery
Chemical Co., Evans City, PA 16033. (b) Earlier examples of this class of
chiral borane reagents can be found in the following: Itsuno, S.; Ito, K.;
Hirao, A.; Nakahama, S. J. Chem. Soc., Chem. Commun. 1983, 469-470.
(12) Kim, H.; Choi, B.; Kwon, K.; Lee, S.; Kwak, H. J.; Lee, C. H.
Biorg. Med. Chem. 2000, 8, 2059-2065.
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Org. Lett., Vol. 2, No. 19, 2000