Synthesis of the shark repellent pavoninin-4

Article abstract of DOI:10.1021/jo051733a

The first synthesis of the shark repellent pavoninin-4, 3, was achieved in 12 steps with 21% overall yield from diosgenin, 8. Key reactions involve an efficient synthesis of the C-15α hydroxyl steroid from a C-16β hydroxyl steroid by an unexpected 1,2-tra

Full text of DOI:10.1021/jo051733a

Synthesis of the Shark Repellent Pavoninin-4
John R. Williams,* Hua Gong, Nathan Hoff, and Olaoluwa I. Olubodun
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122-2585
john.r.williams@temple.edu
Received August 16, 2005
The first synthesis of the shark repellent pavoninin-4, 3, was achieved in 12 steps with 21% overall
yield from diosgenin, 8. Key reactions involve an efficient synthesis of the C-15R hydroxyl steroid
from a C-16â hydroxyl steroid by an unexpected 1,2-transposition strategy, a stereospecific
glycosylation of a hindered C-15R alcohol using glycosyl fluoride as a glycosyl donor and a highly
chemoselective acetylation of the C-26 primary alcohol by catalytic transesterification.
Introduction
It is known that fish belonging to the species Par-
dachirus pavoninus (Soleidae) excrete a mixture of six
steroidal N-acetylglucosaminides, pavoninins-1-6, 1-4
(Figure 1).1 These steroidal N-acetylglucosaminides have
shark-repelling properties.1 It is believed that the pavo-
ninins are potent cell disrupters, which should have
important pharmacological properties. The synthesis of
pavoninin-1, 1a,2 and the aglycones of pavoninin-1, 1a,
and -2, 1b, have been reported.3 Recently, we reported
the synthesis of the aglycone of 26-O-deacetyl pavoninin-
5, 2b.4 The isolation and synthesis of shark-repelling
saponins have recently been reviewed.5 In this article,
we report the first synthesis of pavoninin-4 (3), a saponin
with the monosaccharide N-acetylglucosamine attached
at the C-15R position of the steroid.
FIGURE 1. Pavoninins 1-6 (1-4).
Results and Discussion
reductively eliminated at the end of the synthesis. The
C-15R hydroxyl steroid 5 was prepared from a C-16â
hydroxyl steroid 7 by a 1,2-transposition strategy involv-
ing an unexpected stereospecific reduction of a conjugated
enone. The intermediate 7 was prepared from the com-
mercially available diosgenin, 8.
The synthesis commenced with a Mitsunobu reaction6
on (25R)-5R-cholestane-3â,16â,26-triol (9), which was
available from the naturally abundant steroid source
diosgenin 8 in two steps.7 The reaction afforded the
3R,26-dibenzoate 10 in 85% yield and achieved several
Retrosynthetic analysis for the synthesis of pavoninin-4
(3) is given below, starting from diosgenin, 8 (Scheme
1). The N-acetylglucosamine 6 may be added to a C-15R
hydroxyl steroid, 5, to yield pavoninin-4, 3. To plan for
selective introducing of the C-26 acetate, the sugar
alcohols were protected with benzyl groups that can be
(1) (a) Tachibana, K.; Sakaitani, M.; Nakanishi, K. Science 1984,
226, 703. (b) Tachibana, K.; Sakaitani, M.; Nakanishi, K. Tetrahedron
1985, 41, 1027.
(2) Ohnishi, Y.; Tachibana, K. Bioorg. Med. Chem. 1997, 5, 2251.
(3) Kim, H. S.; Kim, I. C.; Lee, S. O. Tetrahedron 1997, 53, 8129.
(4) (a) Williams, J. R.; Chai, D.; Gong, H.; Zhao, W.; Wright, D.
Lipids 2002, 37, 1193. (b) Williams, J. R.; Chai, D.; Bloxton, J. D., II;
Gong, H.; Solvibile, W. R. Tetrahedron 2003, 59, 3183.
(5) Williams, J. R.; Gong, H. Lipids 2004, 39, 795.
(6) For reviews, see: (a) Mitsunobu, O. Synthesis 1981, 1. (b)
Dembinski, R. Eur. J. Org. Chem. 2004, 2763.
10.1021/jo051733a CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/12/2005
10732
J. Org. Chem. 2005, 70, 10732-10736

Synthesis of the Shark Repellent Pavoninin-4
5R-cholesta-3â,15R,26-triol.7 Regiospecific dehydration of
the hindered C-16â hydroxyl via the bis-protected 16-
mesylate of 10, by Kim’s method8 using NaI in DMF,
yielded the disubstituted C-16 olefin, 11, in 96% yield.
Hydroxylation at C-15R was efficiently introduced by
allylic oxidation at C-15 using chromium trioxide and 3,5-
dimethylpyrazole to yield the 16-en-15-one, 12. Ste-
reospecific Luche9 reduction proceeded quantitatively
from the unexpected â face to yield the 15R allylic alcohol,
13. This result may be explained using molecular model-
ing. When C-16 and C-17 are sp2 hybridized, C-22 of the
cholesterol side chain can move down such that the side
chain can swing under the steroid skeleton and protect
the C-15 from R attack. Subsequent hydrogenation of 13
afforded the saturated alcohol 14. The R-configuration
of the C-15 hydroxyl group was proven by comparison of
14 with its 3â epimer (25R)-5R-cholesta-3â,15R,26-triol,
whose structure had been determined by X-ray analysis.7
The chemical shift for the 15â hydrogen in 14 is a doublet
of triplets (J ) 9.0, 3.2 Hz) at 3.88 ppm, and that for the
3â epimer was a doublet of triplets (J ) 9.1, 3.0 Hz) at
3.91 ppm.7 Thus, the intermediate target molecule pavo-
ninin-4 aglycone 14 was successfully achieved through
a six-step synthesis in 48.5% overall yield from (25R)-
5R-cholestane-3â,16â,26-triol, 9, (Scheme 2).
SCHEME 1. Retrosynthetic Analysis of
Pavoninin-4 (3) from Diosgenin (8)
transformations. The triol 9 C-3 and C-26 hydroxyl
groups were chemoselectively protected, and at the same
time, the C-3 hydroxyl stereochemistry was inverted from
â to R, all in one step. To transpose the C-16â hydroxyl
in 10 to the 15R position, we have reported a successful
six-step method in our synthesis of the aglycone of 26-
O-deacetyl pavoninin-5.4 The C-16 alcohol was oxidized
to the ketone, converted to its silyl ether, and epoxidized
to the 15R-hydroxy-16-ketone. Reduction of the ketone
and chemoselective deoxygenation of the C-16 alcohols
using the Barton deoxygenation reaction afforded the 15R
alcohol.4
With C-15R hydroxyl intermediate 14 in hand, we
turned our attention to attaching the sugar onto the
steroid. A literature survey showed that only a few
synthetic efforts have been devoted to the N-acetylami-
Recently, we developed a very efficient four-step method
for this transposition, via allylic oxidation and subse-
quent stereospecific reduction, in our synthesis of (25R)-
SCHEME 2. Synthesis of the Shark Repellent Pavoninin-4 (3)
J. Org. Chem, Vol. 70, No. 26, 2005 10733

Williams et al.
noglycosylation reaction on a steroid. The synthesis of
15R-hydroxyestrogen 15-N-acetylglucosaminides, by the
Koenigs-Knorr reaction employing cadmium carbonate
as a catalyst, afforded the products in about 30% yield
when the acetochloroglucosamine was used in large
excess.10 Nishizawa reported that thermal glycosylation
of cholesterol with 2-deoxy-2-acetoamino-3,4,6-tri-O-
acetylglucopyranosyl chloride at relatively lower tem-
peratures gave rise to â-glycosides selectively, whereas
higher temperatures favored the R-glycoside.11 Originally,
we planned to use the commercially available glycosyl
donor, N-acetylglucosamine chloride, to attach on our
steroids. Unfortunately, there was no reaction when we
tried to attach 2-deoxy-2-acetoamino-3,4,6-tri-O-acetyl-
glucopyranosyl chloride on the hindered 16â hydroxyl
steroid 10, even though a model study using 5-androsten-
3â-ol-17-one (DHEA) worked well. Kahne reported a new
method for rapid glycosylation of unreactive substrates
using glycosyl sulfoxides as a glycosyl donor,12 and
Tachibana used this methodology to attach a 2-azido-2-
deoxy-D-glucopyranose to the C-7 hydroxyl of a steroid
in the total synthesis of pavoninin-1, 1a.2 However, the
synthesis of the glycosyl donor, 2-azido-3,4,6-tri-O-benzyl-
1,2-dideoxy-1-phenylsulfinyl-D-glucopyranose, would take
eight steps from a commercially available precursor sugar
and requires more steps to convert the azido group into
the N-acetyl group in a later stage of the synthesis of
pavoninin-1. It was necessary to develop another method
to attach N-acetylglycosylamine to the very hindered
C-15 hydroxyl position of a steroid. Recently, Mukaiyama
reported that glycosyl fluorides are very good glycosyl
donors.13a We attempted to convert the glycosyl chloride
directly to a glycosyl fluoride using silver fluoride in dry
acetonitrile,14 but the yield of 2-acetamido-2-deoxy-â-D-
glucopyranosyl fluoride obtained was not as high as
reported. Also, the later deacetylation of the glycosyl
fluoride to replace the acetate protecting groups with
benzyls was difficult to achieve in high yield. Another
commercially available sugar source, 2-acetamido-2-
deoxy-D-glucose, was readily available and was converted
in four steps to 2-acetamido-3,4,6-tri-benzyl-2-deoxy-D-
glucopyranose, 6a, by a known method.15 Reaction of the
2-acetoamido-2-deoxy-3,4,6-tri-benzyl-D-glucopyranose 6a
with DAST afforded the fluoride 6b.16
material. Exclusive formation of the â-glycoside can be
explained by the intramolecular cyclization of the neigh-
boring C-2R acetamide function at the C-1R position,
directing the C-15 alcohol to attack â via an SN2 reaction
to yield the â-glycoside 15. Hydrolysis of C-3 and C-26
benzoyl protecting groups using potassium hydroxide in
methanol gave the expected C-3 and C-26 diols 16. To
selectively introduce the C-26 acetate, we tried Stork’s
condition using acetic anhydride and pyridine17 and
Yamada’s condition using 3-acetyl-1,3-thiazolidine-2-
thione and sodium hydride,18 but in both conditions, the
obtained yields of the C-26 acetate 17 were poor. A high
yield of 17 was obtained by Otera’s transesterification
using vinyl acetate under distannoxane catalysis.19 Depro-
tection of the benzyl ethers using catalytic hydrogenation
afforded pavoninin-4 (3). The spectroscopic data for the
synthetic pavoninin-4 were identical with those reported
for the natural product.1b
In summary, we report the first synthesis of pavo-
ninin-4 in 12 steps in 21% overall yield from com-
mercially available diosgenin. The Mitsunobo reaction
was found to be a good method for highly chemoselective
protection of C-3 and C-26 hydroxyl groups of the 3â,-
16â,26-triol and for simultaneously epimerizing the ster-
eochemistry of the C-3 hydroxyl from â to R. The 1,2-
transposition strategy involving an unexpected stereo-
specific reduction of a C-15,16 conjugated enone has
proven to be an efficient method for synthesis of the
C-15R hydroxyl steroid from a C-16â hydroxyl steroid. A
short method for stereospecific attachment of the N-
acetylglucosamine monosaccharide to a hindered alcohol
was developed by using 2-acetamido-3,4,6-tribenzyl-2-
deoxy-D-glucopyranosyl fluoride as a glycosyl donor. An
efficient method for the chemoselective acetylation of the
C-26 primary alcohol of the steroid in the presence of
N-acetylglucosamine was also reported.
Experimental Section
2-Acetamido-3,4,6-tribenzyl-2-deoxy-D-glucopyrano-
syl Fluoride (6b). 2-Acetamido-3,4,6-tribenzyl-2-deoxy-D-
1
glucopyranose 6a:15 mp 212-214 °C; H NMR δ 2.06 (s, 3H),
3.43-3.44 (m, 1H), 3.73-3.79 (m, 2H), 3.84-3.85 (m, 2H), 3.98
(m, 1H), 4.60-4.72 (m, 4H), 4.84-4.99 (m, 2H), 5.17-5.18 (d,
J ) 3.5 Hz, 1H), 7.30-7.47 (m, 15H); 13C NMR δ 23.1, 55.6,
70.5, 72.0, 74.8, 76.3, 76.5, 80.5, 82.2, 93.3, 129.0, 129.1, 129.4,
129.6, 129.75, 129.82, 139.9, 140.1, 140.5, 173.7; HRMS calcd
for C29H33NO6 (M + Na+) 514.2206, found 514.2215. To the
alcohol 6a (1 g, 2.0 mmol) in a stirred solution of THF (50 mL)
at -30 °C under argon gas was added rapidly 0.31 mL (2.4
mmol, 1.2 equiv) of DAST. The cooling bath was removed
immediately. After 30 min at room temperature, thin-layer
chromatography (TLC) (3:2 toluene/ethyl acetate) indicated
complete reaction. The reaction mixture was cooled to -30 °C,
and methanol (0.3 mL) was added. After evaporation of the
solvent, a normal aqueous workup in chloroform yielded the
crude mixture of fluorides, which were purified by short-path
chromatography (3:2 toluene/EtOAc) and subsequent recrys-
tallization with EtOAc/petroleum ether (1:1). The fluoride 6b
(0.82 g, 82%) was obtained as colorless needles: mp 186-187
°C; 1H NMR δ 1.83 (s, 3H), 3.67-3.70 (m, 1H), 3.71-3.73 (m,
Through the use of the fluoride 6b, glycosylation of the
C-15R hydroxyl intermediate 14, with AgClO4-SnCl2 as
an activator,13b proceeded very successfully to yield the
saponin 15 in 72% yield, plus 15% of recovered starting
(7) Williams, J. R.; Gong, H.; Hoff, N.; Olubodun, O. I.; Carroll, P.
J. Org. Lett. 2004, 6 (2), 269.
(8) Kim, H. S.; Oh, S. H. Bioorg. Med. Chem. Lett. 1993, 3, 1339.
(9) (a) Luche, J.-L. J. Am. Chem. Soc. 1978, 100, 2226. (b) Gemal,
A. L.; Luche, J.-L. J. Am. Chem. Soc. 1981, 103, 5454.
(10) Suzuki, E.; Namba, S.; Kurihara, H.; Goto, J.; Matsuki, Y.;
Nambara, T. Steroids 1995, 60, 277.
(11) Nishizawa, M.; Shimomoto, W.; Momii, F.; Yamada, H. Tetra-
hedron Lett. 1992, 33, 1907.
(12) Kahne, D.; Walker, S.; Cheng, Y.; Van Engen, D. J. Am. Chem.
Soc. 1989, 111, 6881.
(13) For a recent review, see: (a) Mukaiyama, T. Angew. Chem.,
Int. Ed. 2004, 43, 5590. (b) Nicolaou, K. C.; Ueno, H. Preparative
Carbohydrate Chemistry; Hanessian, S., Ed.; Marcel Dekker: New
York, 1997; pp 313-338.
(17) Stork, G.; Takahashi, T.; Kawamoto, I.; Suzuki, T. J. Am. Chem.
Soc. 1978, 100, 8272.
(18) Yamada, S. Tetrahedron Lett. 1992, 33, 2171.
(19) (a) Orita, A.; Mitsutome, A.; Otera, J. J. Org. Chem. 1998, 63,
2420. (b) Orita, A.; Sakamoto, K.; Hamada, Y.; Mitsutome, A.; Otera,
J. Tetrahedron 1999, 55, 2899.
(14) Ballardie, F. W.; Capon, B.; Dearie, W. M.; Foster, R. L.
Carbohydr. Res. 1976, 49, 79.
(15) Hoffmann, M.; Burkhart, F.; Hessler, G.; Kessler, H. Helv.
Chim. Acta. 1996, 79, 1519.
(16) Posner, G. H.; Haines, S. R. Tetrahedron Lett. 1985, 26, 5.
10734 J. Org. Chem., Vol. 70, No. 26, 2005

Synthesis of the Shark Repellent Pavoninin-4
1H), 3.78-3.82 (m, 1H), 3.84-3.86 (m, 1H), 3.94-3.98 (m, 1H),
4.21-4.28 (m, 1H), 4.54-4.67 (m, 4H), 4.85-4.92 (m, 2H),
5.08-5.10 (d, J ) 8.6 Hz, 1H), 5.63 (dd, JH1F ) 53.6 Hz, JH1H2
) 2.4 Hz, 1H), 7.22-7.42 (m, 15H); 13C NMR δ 23.6, 53.0, 68.2,
73.9, 74.8, 75.2, 75.6, 77.1, 78.0, 78.9, 106.2, 108.4, 128.2, 128.3,
128.4, 128.5, 128.6, 128.9, 129.1, 138.1, 138.5, 170.5; HRMS
calcd for C29H32FNO5 (M + Na+) 516.2162, found 516.2150.
128.8, 129.9, 130.9, 131.5, 133.2, 133.3, 166.3, 167.1, 188.9,
208.4; HRMS calcd for C41H52O5 (M + Na+) 647.3712, found
647.3714.
(25R)-5r-Cholestane-16-en-3r,15r,26-triol 3,26-Diben-
zoate (13). To a solution of 12 (100 mg, 0.16 mmol) in THF/
MeOH (2:1) (2 mL) was added cerium trichloride (0.07 g, 0.192
mmol) and NaBH4 (0.008 g, 0.21 mmol). The reaction mixture
was stirred at room temperature for 2 h and then quenched
with water (1 mL), concentrated in vacuo to remove the excess
THF and MeOH, and extracted three times with CH2Cl2. The
organic layer was washed with 0.1 N HCl, dried (Na2SO4),
filtered, and concentrated in vacuo. The residue was flash
chromatographed (silica gel, 10% ethyl acetate/hexanes) to give
(25R)-5r-Cholestane-3r,16â,26-triol 3,26-Dibenzoate (10).
To a solution of triol 97 (1.0 g, 2.4 mmol) in 40 mL of THF at
25 °C was added triphenylphosphine (2.5 g, 9.5 mmol) and
benzoic acid (1.2 g, 9.78 mmol) followed by the dropwise
addition of DIAD (1.5 mL, 7.2 mmol). The reaction was stirred
for 2 h. Then, 20 mL of saturated NaHCO3 solution was added,
and the mixture was extracted with EtOAc (30 mL × 3). The
organic layers were washed with saturated NaHCO3, brine,
and water and dried with anhydrous Na2SO4. Concentration
of the solvent and purification of the residues by flash
chromatography (silica gel, 20% ethyl acetate/hexanes) af-
forded 10 as colorless oil (1.28 g, 85% yield): IR (KBr) 3546,
1716 cm-1; 1H NMR δ 0.78 (s, 3H), 0.80 (s, 3H), 0.90-0.91 (d,
J ) 6.6 Hz, 3H), 0.94-0.95 (d, J ) 6.8 Hz, 3H), 3.99 (m, 1H),
4.15-4.28 (m, 2H), 5.21(s, 1H), 7.35-8.00 (m, 10H); 13C NMR
δ 11.8, 13.7, 17.5, 18.6, 20.9, 21.7, 24.1, 26.7, 28.7, 30.2, 32.3,
33.1, 33.4, 33.6, 34.2, 35.5, 36.3, 36.4, 37.1, 40.5, 40.9, 42.9,
54.7, 54.8, 62.0, 70.32, 71.15, 72.81, 128.73, 129.95, 130.95,
131.62, 132.41, 133.09, 133.23, 166.30, 167.1; HRMS calcd for
C41H56O5 (M + Na+) 651.4025, found 651.4011.
(25R)-5r-Cholest-16-en-3r,26-diol 3,26-Dibenzoate (11).
A solution of methanesulfonyl chloride (0.2 mL, 2.57 mmol)
in dry pyridine (5 mL) was added to a solution of 10 (500 mg,
0.80 mmol) in dry pyridine (10 mL) at 0 °C. The mixture was
kept at 0 °C overnight. The red solution was poured into ice
water, and the resulting mixture was extracted with ether.
The ether extract was washed successively with 2 N cold HCl,
brine, saturated NaHCO3, and water, then dried and concen-
trated to give (25R)-3R,26-dibenzoyloxy-5R-cholest-16â-ol 16-
mesylate. The resulting 16-mesylate was heated with NaI (500
mg, 3.34 mmol) in DMF (20 mL) at 120 °C for 2 h. The mixture
was diluted with H2O and extracted with EtOAc. The organic
layers were washed with saturated NaHCO3 and brine, then
dried and concentrated to give a yellow colored oil, which was
further purified by chromatography (silica gel, hexanes/ethyl
acetate 10:1) to give 11 (466 mg, 96% yield) as colorless oil:
IR (KBr) 1721, 1603 cm-1; 1H NMR δ 0.67 (s, 3H), 0.80 (s, 3H),
0.91-0.92 (d, J ) 7.2 Hz, 3H), 0.93-0.95 (d, J ) 6.8 Hz, 3H),
4.01-4.16 (m, 2H), 5.20 (s, 1H), 5.22 (s, 1H), 7.35-8.00 (m,
10H); 13C NMR δ 11.8, 16.8, 17.5, 21.2, 25.2, 26.8, 28.8, 31.4,
32.3, 32.6, 33.1, 33.5, 34.1, 34.6, 35.6, 37.1, 41.1, 47.6, 55.5,
57.8, 70.3, 71.1, 121.0, 128.7, 130.0, 131.0, 131.6, 133.1, 133.2,
140.1, 161.2, 166.3, 167.1; HRMS calcd for C41H54O4 (M - H+)
609.3944, found 609.3934.
(25R)-3r,26-Dihydroxy-5r-cholest-16-en-15-one 3,26-
Dibenzoate (12). 3,5-Dimethylpyrazole (0.379 g, 3.95 mmol)
was added to a suspension of chromium trioxide (0.395 g, 3.95
mmol) in dry CH2Cl2 (5 mL) at -20 °C under argon. The
resulting mixture was stirred at -20 °C for 0.5 h. A solution
of 11 (100 mg, 0.164 mmol) in dry CH2Cl2 (2 mL) was added
to the obtained dark red solution in one portion, and the
resulting mixture was stirred at -20 °C for 5 h. Then, 5 N
NaOH solution (2 mL) was added, and the mixture was stirred
at 0 °C for 1 h. Extraction with CH2Cl2 (3 × 10 mL) and the
combined extracts were washed with 1 N HCl solution, dried
(Na2SO4), filtered, and concentrated in a vacuum. The residue
was flash chromatographed (silica gel, 20% ethyl acetate/
hexanes) to give 12 as colorless oil (62 mg, 60% yield): IR (KBr)
1714 cm-1; 1H NMR δ 0.77 (s, 3H), 0.93 (s, 3H), 0.93-0.95 (d,
J ) 7.2 Hz, 3H), 1.02-1.03 (d, J ) 6.3 Hz, 3H), 4.02-4.13 (m,
2H), 5.22 (s, 1H), 5.56 (s, 1H), 7.36-7.98 (m, 10H); 13C NMR
δ 11.9, 17.4, 21.8, 24.1, 25.3, 26.6, 28.3, 32.8, 32.9, 33.2, 33.3,
33.4, 33.5, 33.9, 36.6, 36.7, 41.1, 47.5, 55.4, 64.3, 70.1, 124.8,
13 as a colorless oil (98 mg, 98% yield): IR (KBr) 1721 cm-1
;
1H NMR δ 0.75 (s, 3H), 0.83 (s, 3H), 0.94 (d, J ) 3.3 Hz, 3H),
0.95 (d, J ) 3.2 Hz, 3H), 4.02-4.15 (m, 2H), 4.44 (m, 1H), 5.19
(s, 1H), 5.22 (s, 1H), 7.35-7.99 (m, 10H); 13C NMR δ 11.9, 17.5,
20.0, 21.1, 22.2, 25.2, 26.7, 28.7, 32.3, 33.0, 33.1, 33.4, 34.0,
34.7, 35.5, 36.6, 37.0, 41.0, 48.2, 55.3, 66.2, 70.2, 71.0, 78.1,
126.2, 128.8, 129.9, 131.6, 133.1, 133.2, 162.0, 166.3, 167.1;
HRMS calcd for C41H54O5 (M + Na+) 649.3869, found 649.3869.
(25R)-5r-Cholestane-3r,15r,26-triol 3,26-Dibenzoate
(14). To 20 wt % Pd(OH)2 on carbon (5 mg) was added several
drops of ethyl acetate to wet the catalyst. Subsequently, a
solution of 13 (30 mg, 0.048 mmol) in ethyl acetate (1 mL) was
added. The flask was evacuated (40 Torr) and flushed three
times with hydrogen. The reaction mixture was then stirred
vigorously under hydrogen for 3 h. It was then filtered through
a pad of Celite, and the filtrate was concentrated. The residue
was purified by flash chromatography (silica gel, hexanes/
EtOAc, 10:1) to afford 14 as colorless oil (30 mg, 98% yield):
IR (KBr) 3421, 1717 cm-1; 1H NMR δ 0.68 (s, 3H), 0.86 (s, 3H),
0.88 (d, J ) 6.1 Hz, 3H), 0.99 (d, J ) 6.7 Hz, 3H), 3.88 (dt, J
) 9.0, 3.2 Hz, 1H), 4.16-4.20 (m, 2H), 5.26 (s, 1H), 7.41-8.05
(m, 10H); 13C NMR δ 11.9, 13.8, 17.4, 18.9, 21.1, 23.6, 26.7,
28.6, 32.7, 33.1, 33.4, 33.6, 34.3, 35.4, 35.6, 36.3, 40.5, 40.7,
41.0, 44.5, 54.2, 54.7, 64.3, 70.3, 71.0, 74.2, 128.8, 130.0, 131.0,
131.6, 133.1, 133.2, 166.3, 167.1; HRMS calcd for C41H56O5 (M
- H+) 627.4050, found 627.4026.
(25R)-15r-(2-Acetylamino-3,4,6-tri-O-benzyl-2-deoxy-â-
D-glucopyranosyloxy)-3r-benzoyloxy-5r-cholestan-26-
yl Benzoate (15). To a suspension of AgClO4 (12 mg, 0.06
mmol), SnCl2 (11 mg, 0.06 mmol), and crushed 4-Å molecular
sieves (150 mg, dried) in anhydrous CH2Cl2 (3.5 mL) under
argon at -15 °C was added C-15 alcohol 14 (50 mg, 0.08 mmol)
in CH2Cl2 (1 mL). A solution of the 2-acetylamido-3,4,6-tri-O-
benzyl-2-deoxy-D-glucopyranosyl fluoride 6b (50 mg, 0.10
mmol) in CH2Cl2 (1 mL) was added, and stirring was continued
at 0 °C for 16 h. The reaction mixture was diluted with CH2-
Cl2 (30 mL) and filtered through Celite. The filtrate was
washed with saturated aqueous NaHCO3 solution (5 mL) and
brine (5 mL) and dried (anhydrous Na2SO4). Evaporation of
the solvent and purification by flash chromatography (silica
gel, 20% ethyl acetate/hexanes) afforded 15 (65 mg, 72% yield)
as a solid (about 10 mg unreacted 14 was recovered): mp 73-
75 °C; IR (KBr) 3299, 1717, 1654 cm-1; 1H NMR δ 0.59 (s, 3H),
0.75 (s, 3H), 0.81 (d, J ) 2.6 Hz, 3H), 0.85-0.86 (d, J ) 6.7
Hz, 3H), 1.70 (s, 3H), 3.53 (m, 1H), 3.64-3.66 (m, 4H), 3.94-
3.96 (m, 2H), 4.04 (m, 1H), 4.44-4.77 (m, 6H), 5.20-5.22 (m,
1H), 5.30 (m, 1H), 7.15-7.23 (m, 15H), 7.35-7.98 (m, 10H);
13C NMR δ 11.9, 13.7, 17.3, 18.8, 21.1, 24.0, 26.7, 29.2, 32.6,
33.1, 33.5, 33.6, 34.2, 35.5, 35.9, 36.3, 39.5, 40.4, 40.6, 43.1,
54.2, 54.5, 58.4, 61.0, 69.7, 70.4, 71.0, 74.3, 75.1, 75.2, 77.1,
79.4, 81.0, 84.2, 101.5, 127.9, 128.0, 128.1, 128.3, 128.76,
128.84, 129.9, 130.9, 131.5, 133.2, 138.5, 138.8, 139.0, 166.4,
167.1, 170.7; LRMS calcd for C70H87NO10 (M + Na+) 1125,
found 1125.1.
(25R)-3r,26-Dihydroxy-5r-cholestan-15r-yl-2-(acetyl-
amino)-3,4,6-tri-O-benzyl-2-deoxy-â-D-glucopyranoside
(16). To a solution of 15 (100 mg, 0.09 mmol) in 1:1 MeOH/
CH2Cl2 (20 mL) was added KOH-MeOH (1 M, 10 mL). The
solution, after refluxing for 12 h, was cooled to room temper-
J. Org. Chem, Vol. 70, No. 26, 2005 10735

Williams et al.
ature, evaporated, and neutralized with 2 M HCl solution. The
mixture was extracted with CH2Cl2 (10 mL × 3) and dried
(anhydrous Na2SO4). Evaporation of the solvent and purifica-
tion by flash chromatography (silica gel, 50% ethyl acetate/
hexanes) afforded 16 (72 mg, 90% yield) as a white solid: mp
Pavoninin-4 (3). A solution of acetate 17 (20 mg, 0.02
mmol) in MeOH (5 mL) was stirred with 10 wt % Pd/C (8 mg)
at room temperature under a hydrogen atmosphere overnight.
The catalyst was removed by filtration, and the solvent was
removed by evaporation to afford pavoninin-4 (3) (13.6 mg,
137-139 °C; IR (KBr) 3290, 1654 cm-1 1H NMR δ 0.66 (s,
;
96% yield) as a white solid, without further purification: [R]20
D
+28° (c 0.4, EtOH); mp 134-136 °C; 1H NMR (CD3OD) δ 0.60
(s, 3H), 0.72 (s, 3H), 0.81 (d, J ) 5.6 Hz, 3H), 0.84 (d, J ) 4.4
Hz, 3H), 1.68 (s, 3H), 1.94 (s, 3H), 2.08 (m, 1H), 3.13 (m, 1H),
3.20 (m, 1H), 3.34 (m, 1H), 3.47 (m, 1H), 3.57-3.61 (m, 2H),
3.73-3.78 (m, 2H), 3.84-3.86 (m, 2H), 4.28 (d, J ) 8.3 Hz,
1H); 13C NMR (CD3OD) δ 12.2, 14.1, 17.5, 19.4, 21.2, 22.2, 23.7,
24.7, 30.0, 30.6, 33.9, 34.2, 34.3, 35.1, 34.0, 37.2, 37.4, 37.6,
40.4, 40.5, 41.9, 44.3, 55.6, 56.2, 58.2, 62.7, 63.4, 67.6, 71.1,
72.6, 76.5, 78.0, 85.7, 104.3, 173.6, 173.8; HRMS calcd for
C37H63NO9 (M + Na+) 688.4401, found 688.4394.
3H), 0.77 (s, 3H), 0.84-0.85 (d, J ) 4.7 Hz, 3H), 0.90-0.92 (d,
J ) 5.7 Hz, 3H), 1.81 (s, 3H), 3.23-3.77 (m, 10H), 4.03 (s, 1H),
4.20-4.25 (m, 1H), 4.54-4.85 (m, 8H), 5.52-5.54 (d, J ) 7.6
Hz, 1H), 7.22-7.34 (m, 15H); 13C NMR δ 11.6, 13.7, 16.9, 18.8,
21.0, 23.9, 24.1, 29.4, 32.7, 33.9, 35.5, 35.8, 36.2, 36.5, 39.3,
39.6, 40.4, 43.1, 54.0, 54.4, 58.8, 61.0, 66.9, 68.8, 69.8, 74.2,
75.1, 75.2, 75.3, 79.5, 80.8, 84.0, 101.1, 128.0, 128.1, 128.3,
128.8, 138.5, 138.9, 139.0, 170.7; HRMS calcd for C56H79NO8
(M + Na+) 916.5703, found 916.5720.
(25R)-15r-(2-Acetylamino-3,4,6-tri-O-benzyl-2-deoxy-â-
D-glucopyranosyloxy)-3r-benzoyloxy-5r-cholestan-26-
yl Acetate (17). To a solution of 16 (50 mg, 0.06 mmol) in 2
mL of CH2Cl2 and 5 mL of vinyl acetate was added 1,3-
dichlorodistannoxane (1.2 mg, 2.2 × 10-3 mmol). The mixture
was stirred at room temperature overnight (12 h). After
evaporation, the crude mixture was chromatographed on a
silica gel column (50% ethyl acetate/hexanes) to afford 17 (42
Acknowledgment. Financial support for this re-
search was provided by a grant from the Temple
University Research Incentive Fund, GlaxoSmithKline,
Pfizer, Bristol-Myers Squibb, and Merck. N. H. and O.
O. were supported in part by the Howard Hughes
Medical Institute grant to the Undergraduate Biological
Sciences Education Program at Temple University. We
thank Dr. Jeffrey Honovich of Drexel University for the
high-resolution mass spectra.
mg, 80% yield) as colorless oil: IR (KBr) 3288, 1737, 1654 cm-1
;
1H NMR δ 0.58 (s, 3H), 0.69 (s, 3H), 0.75-0.76 (d, J ) 6.7 Hz,
3H), 0.79-0.80 (d, J ) 5.6 Hz, 3H), 1.74 (s, 3H), 1.94 (s, 3H),
3.15 (m, 1H), 4.16-4.20 (m, 2H), 3.14 (m, 1H), 3.44-3.79 (m,
7H), 3.96 (s, 1H), 4.14 (m, 1H), 4.46-4.61 (m, 4H), 4.71-4.78
(m, 3H), 5.40 (d, J ) 7.6 Hz, 1H), 7.15-7.25 (m, 15H); 13C NMR
δ 11.6, 13.7, 17.1, 18.8, 21.0, 21.4, 23.9, 24.1, 29.4, 32.7, 32.9,
34.2, 35.5, 35.8, 36.3, 36.5, 39.3, 39.6, 40.4, 43.1, 54.0, 54.4,
58.8, 61.0, 66.9, 69.7, 70.0, 74.3, 75.1, 75.3, 79.5, 80.8, 84.0,
101.2, 127.9, 128.2, 128.3, 128.77, 128.83, 138.5, 138.8, 139.0,
170.7, 171.7; HRMS calcd for C58H81NO9 (M + Na+) 958.5809,
found 958.5822.
Supporting Information Available: 1H and 13C NMR
spectra for all synthesized compounds, 6a and b, 10-17, and
pavoninin-4. This material is available free of charge via the
Internet at http://pubs.acs.org.
JO051733A
10736 J. Org. Chem., Vol. 70, No. 26, 2005