Bengazoles C-G from the sponge Jaspis sp. Synthesis of the side chain and determination of absolute configuration

Article abstract of DOI:10.1021/jo952261a

Five new antifungal bengazoles (C-G) were isolated and fully characterized from a marine sponge of the genus Jaspis sp. Bengazoles C-G, together with the known bengazoles A and B, comprise a homologous series of n, iso, and anteiso fatty acid esters (C₁₃-C₁₆) of the same heterocyclic bis(oxazolyl)methanol parent. The complete relative and absolute configurations of the bengazoles were determined by application of the modified Mosher method and interpretation of exciton coupling in the CD spectra of the tetra-p-bromobenzoate derivatives of bengazole A and that of a model tetrol synthesized in seven steps from L-fucose.

Full text of DOI:10.1021/jo952261a

J . Org. Chem. 1996, 61, 4073-4079
4073
Ben ga zoles C-G fr om th e Sp on ge J a spis sp . Syn th esis of th e Sid e
Ch a in a n d Deter m in a tion of Absolu te Con figu r a tion †
Philip A. Searle,1 Rowena K. Richter,2 and Tadeusz F. Molinski*
Department of Chemistry, University of California, Davis, California 95616
Received December 22, 1995X
Five new antifungal bengazoles (C-G) were isolated and fully characterized from a marine sponge
of the genus J aspis sp. Bengazoles C-G, together with the known bengazoles A and B, comprise
a homologous series of n, iso, and anteiso fatty acid esters (C13-C16) of the same heterocyclic bis-
(oxazolyl)methanol parent. The complete relative and absolute configurations of the bengazoles
were determined by application of the modified Mosher method and interpretation of exciton coupling
in the CD spectra of the tetra-p-bromobenzoate derivatives of bengazole A and that of a model
tetrol synthesized in seven steps from L-fucose.
An increasing number of cytotoxic and antifungal
oxazoles have been reported in recent years from marine
invertebrates.3-6 Recent examples include the cytotoxic
natural products kabiramide C,7,8 hennoxazole,9 phor-
boxazoles A and B,10 and theonezolides A-C.11,12 While
the structures of most of these oxazoles have polyketide
components, the bengazoles stand out as unique bis-
(oxazoles) containing a carbohydrate-like polyol side
chain. Bengazole A (1a ) was first isolated by Crews and
co-workers from a Pacific Choristid sponge along with
the homolog bengazole B (1b), both of which exhibited
anthelminthic activity against Nippostrongylus brazilien-
sis.13 In recent work from our laboratory, we showed that
1a ,b are also potent ergosterol-dependent antifungal
agents; their activity against Candida albicans and
Saccharomyces cerevisiae is comparable with that of
amphotericin B.14 This preliminary report also revealed
five additional bengazoles (1c-g) from a sponge identi-
fied as J aspis sp. from the Indo-Pacific region (Figure
1). The new bengazoles are homologous fatty acid esters
F igu r e 1. Bengazoles A-G (1a -g) and model compound 2.
Bengazole B was isolated as an inseparable 5/1 mixture of iso
and anteiso 15:0 fatty acid esters.
of a heterocyclic nucleus comprised of a bis(oxazolyl)-
methanol further substituted with a hexanetetrol side
chain, reminiscent of a carbohydrate analog. Subse-
quently, two additional reports appeared describing C10
deoxy analogs of 1a . Bengazoles C2, C3, C4, D2, D3, and
D415 are antitumor compounds that lack the C10 hydroxyl
of 1a , but are acylated as myristate (C14) or pentade-
canoate esters at one of the side chain hydroxyl groups.
Digonazole,16 another cytotoxic member of the bengazole
family, is an homologous O-C6 eicosanoate ester (n-C20)
of bengazoles C2-D4. The structures of the bengazole
family of alkaloids were solved by a combination of
spectroscopic methods and chemical degradation, but
there is ambiguity in their stereochemistry.
† This paper is dedicated to Dr. David J . Collins (Monash University)
on the occasion of his 65th birthday.
X Abstract published in Advance ACS Abstracts, May 15, 1996.
(1) Present address: Harbor Branch Oceanographic Institution, Inc.,
Division of Biomedical Marine Research, Fort Pierce, FL 34946.
(2) Present address: Shaman Pharmaceuticals, 213 East Grand
Ave., South San Franciso, CA 94080.
While the relative stereochemistry of the C1-C6 side
chain in 1a was defined by Crews et al.,13 the configu-
ration at C10 relative to the side chain and the absolute
configuration were unassigned leaving the absolute con-
figuration indeterminate among four possible stereoiso-
mers. In order to pursue structure-activity studies
related to non-polyene antifungal compounds, we re-
quired the absolute configuration of 1a . In this report
we reveal characterization of 1c-g14 and unambiguous
determination of the complete relative and absolute
configurations of all stereogenic centers in bengazoles as
depicted in 1. The C10 absolute configuration was
elucidated by modified Mosher ester method while the
C2-6 absolute stereochemistries were determined by
(3) Lewis, J . R. Nat. Prod. Rep. 1994, 11, 395-418.
(4) Lewis, J . R. Nat. Prod. Rep. 1995, 12, 135-163.
(5) Faulkner, D. J . Nat. Prod. Rep. 1994, 11, 355-395.
(6) Faulkner, D. J . Nat. Prod. Rep. 1995, 12, 223-269.
(7) Matsunaga, S.; Fusetani, N.; Hashimoto, K.; Koseki, K.; Noma,
M. J . Am. Chem. Soc. 1986, 108, 847-849.
(8) Kernan, M. R.; Molinski, T. F.; Faulkner, D. J . J . Org. Chem.
1988, 53, 5014-20.
(9) Ichiba, T.; Yoshida, W. Y.; Scheuer, P. J .; Higa, T.; Gravalos, D.
G. J . Am. Chem. Soc. 1991, 113, 3173-3174.
(10) Searle, P. A.; Molinski, T. F. J . Am. Chem. Soc. 1995, 117,
8126-8131.
(11) Kobayashi, J .; Kondo, K.; Ishibashi, M.; Wa¨lchli, M. R.; Naka-
mura, T. J . Am. Chem. Soc. 1993, 115, 6661-6665.
(12) Kondo, K.; Ishibashi, M.; Kobayashi, J . Tetrahedron 1994, 50,
8355-8362.
(13) Adamczeski, M.; Quin˜oa`, E.; Crews, P. J . Am. Chem. Soc. 1988,
110, 1598-1602.
(14) Molinski, T. F. J . Nat. Prod. 1993, 56, 1-8.
(15) Rodriguez, J .; Nieto, R. M.; Crews, P. J . Nat. Prod. 1993, 56,
2034-2040.
(16) Rudi, A.; Kashman, Y.; Benayahu, Y.; Schleyer, M. J . Nat. Prod.
1994, 57, 829-832.
S0022-3263(95)02261-4 CCC: $12.00 © 1996 American Chemical Society

4074 J . Org. Chem., Vol. 61, No. 12, 1996
Searle et al.
) 11.4, 7.2, 2.5 Hz). The 13C NMR chemical shifts of the
isopropylidene methyl groups (δ 19.3 q, 26.9 q)17 also
supported a syn configuration at C4,6 and a threo at
configuration C2,3. Although the C3,4 relationship could
not be confidently assigned on the basis of the vicinal
H3,4 coupling alone (J ) 7.2 Hz), subsequent 1H NMR
measurements on the model compound 2 (see below) and
its diacetonide 18 revealed this to be 3,4-erythro in
agreement with the assignment of Crews.13
The opportunity now presented itself to prepare
discrete crystalline O-C10 derivatives of 4 and 5 in order
to address the stereochemical issue by single-crystal
X-ray crystallography. We prepared various derivatives
including three characterized p-bromobenzoate esters
(6-8), two (-)-(R)-(1-naphthylethyl)urethanes, one
(1S)-(-)-camphanate ester, and a cyclic bis(p-bromo-
phenyl)boronate ester (the latter four are not described
here), but to no avail; in our hands, these compounds
produced crystals of unsuitable dimensions or failed to
crystallize at all. We turned instead to chemical and
chiroptical correlation.
Ta ble 1. Abu n d a n ce a n d HRF ABMS Mea su r em en ts of
Ben ga zoles 1a -g fr om J a spis sp .
% dry
name
formula
weight m/z (MH+) ∆mmu
bengazole A (1a ) C27H44N2O8 0.27
525.3176
539.3305
511.3019
525.3165
539.3326
553.3481
553.3481
-2.7
2.7
0.0
1.1
0.6
0.8
0.8
bengazole B (1b)
bengazole C (1c)
bengazole D (1d )
bengazole E (1e)
C
C
C
C
C
C
28H46N2O8 0.14
26H42N2O8 0.007
27H44N2O8 0.022
28H46N2O8 0.043
29H48N2O8 0.027
29H48N2O8 0.027
bengazole F
(1f)
bengazole G (1g)
interpretation of the exciton coupling in the circular
dichroism (CD) spectra of the tetra-p-bromobenzoate
esters prepared from 1a and synthetic model compound
2, synthesized stereoselectively from L-fucose in seven
steps. Knowledge of the correct configuration of 1a now
allows refinement of the structure-activity relationship
(SAR) models for the antifungal mechanism of action of
bengazoles as well as selection of correct starting materi-
als from the chiral pool for enantioselective total syn-
thesis of 1a .
Resu lts a n d Discu ssion
An ethanol extract of J aspis sp. from the Great Barrier
Reef exhibited potent antifungal activity against C.
albicans and S. carlbergensis. The sponge was exhaus-
tively extracted with methanol, and the antifungal
compounds were isolated by solvent partition followed
by silica gel flash chromatography and C18 reversed phase
HPLC (MeOH/H2O 90:10) to give pure bengazoles A-G
(1a -g, see Table 1). The identities of 1a and 1b were
established by careful comparison of spectroscopic data
(1H and 13C NMR, FABMS) with published values,13 and
the structures of the new bengazoles were determined
by a combination of FABMS and 1H and 13C NMR
1
spectroscopies. The H NMR spectra of the new benga-
zoles were identical with each other in the downfield
region of δ 3-8. The consistent appearance of the H10
singlet at δ 7.1 showed that C10 was acylated in each
compound. Accordingly, we surmised that the com-
pounds differed only in the fatty acid moiety at C10.
Indeed, ammoniolysis (NH3, MeOH) of the mixture of
1a -g gave only one alkaloid, the pentol 3. Methanolysis
of each pure bengazole A-G (HCl, MeOH, 60 °C) gave
the corresponding fatty acid methyl ester (FAME) which
was analyzed by GCMS with single-ion monitoring of the
M - 74 peak (M - C3H6O2, McLafferty rearrangment)
and comparison of retention times with a commercial
standard mixture of bacterial FAMEs. The bengazole
FAMEs varied in carbon chain length from C12 to C18 and
belonged to the n, iso, or anteiso series. HRFABMS (see
Table 1) and 1H NMR spectra of pure 1a -g were
consistent with FAME analysis.
With 5 in hand, the absolute configuration at C10 could
be addressed conveniently using Kakisawa’s modification
of the Mosher method.18 Separate treatment of 5 with
either (R)- or (S)-MTPA (DCC, CH2Cl2, Et3N) gave the
Mosher esters 9a (65%) and 9b (46%), respectively. The
1
measured ∆δ ) δS - δR for H signals in the diastereo-
Crews et al. proposed the 2S*,3R*,4S*,6R* relative
configuration for the carbohydrate side chain of 1a using
meric pair 9a ,b (Figure 2) conformed to the configura-
tional model of Kakisawa18 and revealed the 10S config-
uration.
1
arguments based on NOE, vicinal H coupling constant
analysis of a degradation product, and comparison with
simple tetrose models.13 We were able to verify this by
chemical transformations. Treatment of 1a with 2,2-
dimethoxypropane and p-toluenesulfonic acid (p-TSA) (50
°C) gave 4 as the only acetonide (80%) which was
ammoniolyzed (NH3, MeOH, 87%) to provide alcohol 5.
The Mosher ester method was not appropriate for the
C2-6 configurations due to anticipated complexity in
interpretation of overlapping 1H signals in a heavily
anisotropic tetra-MTPA derivative. Instead, we con-
verted the mixture 1a -g into the corresponding tetra-
1
The H NMR spectrum of 5 was consistent with a chair
(17) Rychnovsky, S. D.; Rogers, B.; Yang, G. J . Org. Chem. 1993,
58, 3511-3515.
(18) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J . Am.
Chem. Soc. 1991, 113, 4092-4096.
conformation for the dioxane ring with equatorial sub-
stituents at C4 and C6 inferred from axial couplings for
H6 (δ 4.97, dd, J ) 11.8, 2.1 Hz) and H4 (δ 3.94, ddd, J

Synthesis of the Side Chain of Bengazoles C-G
J . Org. Chem., Vol. 61, No. 12, 1996 4075
Sch em e 1
F igu r e 2. MTPA ester analysis according to the modified
Mosher-Kakisawa method (see text). Values are derived from
∆δ ) δS - δR , where δS and δR denote 1H NMR chemical shifts
of (S)- and (R)-MTPA esters 9a and 9b, respectively. Units
shown are parts per billion (∆δ ppm × 103). Signals shown
with an asterisk (*) could not be confidently assigned and so
are depicted as interchangeable with the range of possible
values from -120 to -139 ppb.
a
a, BnOH, HCl, 80%; b, Me2C(OMe)2, p-TSA, acetone, 97%; c,
p-bromobenzoate 10 (mixture of fatty acids at C10) and
exploited the strongly split Cotton effects in the CD
spectrum.19,20 Nakanishi and co-workers have reported
the CD exciton coupling for chromophoric derivatives of
a variety of configurationally defined alditols and skipped
polyols,21-24 but CD data for the required modelssa
hexose with lyxo C2,3,4 tri-p-bromobenzoate and with
both C4,6-syn configurationsswere not available. In
principle, one could predict the expected CD curve of 10
by extrapolating these results, but in order to avoid
ambiguity we chose instead to prepare model compound
2 and compare the corresponding tetra-p-bromobenzoate
11 with 10. Two assumptions were made in the choice
of the model for CD comparison. First, the replacement
of the oxazole, attached to the side chain at C6, with a
phenyl group was an acceptable substitution because
both alkylbenzenes and 4-alkyloxazoles are chromophores
with relatively weak charge-transfer electric transition
dipole moments,20 but it also simplified the synthesis of
the model. Second, the perturbation of the tetra-p-
bromobenzoate manifold in 10 by the second oxazole ring
and the fatty ester side chains was expected to be
insignificant compared to that of the stronger intra-side
chain exciton coupling. Our experience shows that
relatively weak split CD effects are found in bis(oxazole)s
such as bengazole A (λ 231 nm, ∆ꢀ -1.55; 202, +3.89)
and even the tris(oxazole) kabiramide C.25 Because the
C2-C4 fragment of the bengazole side chain possessed
the lyxo configuration found in 2-deoxyfucose and related
sugars, we selected L-fucose as the starting material for
synthesis of 2.26
NaH, CS2, MeI, THF, 98% d, H3PO2, Et3N, AlBN, dioxane, reflux,
74%.
rous acid in the presence of triethylamine27 to afford the
differentially protected L-2-deoxyfucose derviative 15
(74%). Samples of the product anomers 15R and 15â
were separated and characterized, but it was more
convenient to carry through the mixture. Removal of the
O-benzyl group from 15 (Pd(OH)2, H2, 1 atm, 77%) gave
3,4-isopropylidene-2-deoxy-L-fucose (16). Treatment of 16
with phenyllithium (5 equiv, THF, -78 °C, Scheme 2)
gave a 2.4/1 mixture of two epimeric diol acetonides 17a ,b
(86%) which was separated by preparative HPLC (silica,
1:1 n-hexane/EtOAc). As expected, the H1 signal of the
major C1 epimer 17a (δ 4.90, dd, J ) 8.5, 4.5 Hz, 1H)
differed only slightly from that of 17b (δ 4.98, dd, J ) 9,
3.2 Hz, 1H). Nevertheless, we were able to show that
the relative configuration of the newly created stereogenic
center C1 in 17a was the same as that of C6 in bengazole
A as follows. Deprotection of acetonide (-)-17a (Dowex
1
50-X8, THF/H2O, 85%) provided tetrol 2 with vicinal H
coupling constants (CD3OD) similar to those of 1a .
Further transformation of 2 to diacetonide 18 (2,2-
dimethoxypropane, p-TSA, acetone, 74%) locked the C1
phenyl susbstituent to the 1,3-dioxane ring in an equato-
rial position, allowing direct comparison of 5 and 18
(Table 2). Interpretation of the COSY and the decoupled
spectra of 18 allowed the assignment of respective vicinal
1H coupling constants which were identical with those
of 5. Note that the H3,4 vicinal coupling observed in
L-fucose-derived 18 (J 3,4 ) 7.0 Hz) independently supports
the 3,4-erythro configuration (bengazole numbering) as-
signed to 1a 13 (J 3,4 ) 7.2 Hz). The trend for larger
couplings in erythro derivatives (J ) 6.5-7.1 Hz) com-
pared to their threo isomers (J ) 3.6-4.7 Hz) has been
well established in closely related acyclic polyol deriva-
tives.22 Because the configuration of the other centers
in 17a are conserved from the starting material, it is
proven that the relative stereochemistries in model tetrol
2 and bengazole (1a ) are identical; however, the absolute
configurations are antipodal as demonstrated below.
The bengazole mixture 1a -g and pure 2 were smoothly
converted (p-bromobenzoyl chloride, DMAP, pyridine, 25
°C) to the tetra-p-bromobenzoate derivatives 10 and 11
(25 and 91%, respectively). The circular dichroism
spectrum of bengazole A derivative 10 showed, as ex-
pected, complex split Cotton effects due to exciton
coupling among the four p-bromobenzoate groups (Figure
L-Fucose was converted (Scheme 1) into benzyl fucopy-
ranoside 12 (BnOH, HCl, 0 °C, mixture of anomers, 80%)
followed by protection of the 3,4-dihydroxyl group as the
acetonide 13 (2,2-dimethoxypropane, p-TSA, 97%). Com-
pound 13, as a 5/1 mixture of â/R anomers, was carried
through to the xanthate ester 14 (NaH, CS2, MeI, 98%)
followed by Barton deoxygenation using hypophospho-
(19) Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy:
Exciton Coupling in Organic Stereochemistry; University Science
Books: Mill Valley, CA, 1983; p 460.
(20) Circular Dichroism: Principles and Applications; Nakanishi,
K., Berova N., Woody, R. W., Eds.; VCH: New York, 1994; p 570.
(21) Wiesler, W. T.; Nakanishi, K. J . Am. Chem. Soc. 1989, 111,
3446-3447.
(22) Wiesler, W. T.; Nakanishi, K. J . Am. Chem. Soc. 1990, 112,
5574-5583.
(23) Zhao, P.; Zhao, N.; Rele, D. N.; Berova, N.; Nakanishi, K. J .
Am. Chem. Soc. 1993, 115, 9313-9314.
(24) Zhou, P.; Berova, N.; Wiesler, W. T.; Nakanishi, K. Tetrahedron
1993, 49, 9343-9352.
(25) Molinski, T. F. Unpublished results.
(26) The choice of L- or D-fucose was arbitrary at this point; however,
L-fucose was the less expensive enantiomer.
(27) Barton, D. H.; J ang, D. O.; J aszberenyi, J . C. J . Org. Chem.
1993, 58, 6838-6842.

4076 J . Org. Chem., Vol. 61, No. 12, 1996
Searle et al.
Sch em e 2
F igu r e 3. Circular dichroism spectra of tetra-p-bromoben-
zoates 10 and 11 in MeCN.
(C48H33N2O12Br5, HRFABMS found 1224.8029 (MH+),
∆mmu 1.9) was also measured. We were reassured to
find the CD spectrum of 8 had essentially the same form
as that of 10, albeit with diminished magnitudes for the
Cotton effects (λ 252 (∆ꢀ -2.7), 236 (+10.2), 208 (+8.7),
198 (-0.2) nm). The bengazole side chain is, thus,
stereochemically related to D-fucose, and the complete
absolute configuration of 1a is now revealed as
2R,3S,4R,6S,10S. Given that the homologs 1b-g pro-
duce only one bis(oxazole), the pentol 3, upon ammoni-
olysis of the fatty acid side chains, the C2-6 configura-
tions in all bengazoles A-G (1a -g) must be identical.28
Biologica l Act ivit y. Bengazoles 1c-g were ap-
proximately equipotent with 1a and 1b in agar disk
diffusion antifungal assay against C. albicans. All gave
zones of inhibition of 9-10.5 mm at 0.5 µg/disk. In broth
dilution assays, bengazole E (1e) gave minimum inhibi-
tory concentrations (MICs) of 1 µg/mL against C. albicans
(c.f. amphotericin B, 0.3 µg/mL) and >100 µg/mL against
S. carlsbergensis. The ergosterol-dependent activity of
1a ,b has already been described14 and suggests a mode
of action for bengazoles that is shared with amphotericin
B. What remains is identification of the minimum
pharmacophore of the bengazole structure that accounts
for antifungal activity, although clearly the fatty acid side
chain is important.29
a
a, Pd(OH)2, H2, 1 atm, EtOH; b, PhLi, THF, -78° to 0 °C, 86%;
c, Dowex 50-X8, THF, H2O, 90%; d, p-BrBzCl, py, DMAP, 91%; e,
Me2C(OMe)2, acetone, p-TSA, 74%.
Ta ble 2. Com p a r ison of Vicin a l Con sta n ts (J ) for
Ben ga zole A Der iva tive 5 a n d Mod el Com p ou n d 18
(Note: or d er of n u m ber in g is d iffer en t for 5 a n d 18)
Con clu sion
The notable biological activity of alkaloids in the
bengazole family and the need for sufficient quantities
for SAR and in vivo studies makes these natural products
important targets for total synthesis. The absolute
configuration of C10 in 1a is S, and the side chain
configuration is 2R,3S,4R,6S by excition coupling of
p-bromobenzoate derivatives. The latter approach now
makes it a simple matter to confirm the side chain
configuration of digonazole16 and other bengazoles.15
Synthesis of 17a and 2 models a side chain synthesis of
1a , with stereoselective control at C6, and presages our
approach to the total synthesis of bengazole A based on
oxazole C4 anion addition to the protected side chain
precursor 16.30 We have embarked upon the completion
compound 5 (CDCl3)
compound 18 (d6-acetone)
no.
δ
mult
d
J (Hz)
no.
δ
mult
d
J (Hz)
1
2
3
4
1.34
6.1
6
5
4
3
1.28
6.0
4.00 dq
3.44 dd
3.94 ddd
7.6, 6.1
7.6, 7.2
3.99 dq
3.37 dd
4.08 ddd
7.7, 6.0
7.7, 7.0
11.5, 7.0, 2.5
12.9, 2.5, 2.5
12.9, 11.5, 11.5
11.5, 2.5
11.4, 7.2, 2.5
13.0, 2.5, 2.1
13.0, 11.8, 11.4 2â 1.45 ddd
11.8, 2.1 5.04 dd
5R 2.10 ddd
2R 1.96 ddd
5â 1.69 ddd
6
4.97 dd
1
3). The CD of 10 showed a strong negative Cotton effect
at λ 252 nm (∆ꢀ -14.8) followed by two positive Cotton
effects at λ 235 (+17.3) and 208 (+12.5) nm and a smaller
negative Cotton effect at λ 196 (-10) nm. The CD
spectrum of model compound 11 (λ 252 (∆ꢀ +6.5), 234
(-19.5), 207 (-9.8), 197 (+2.5) nm) was essentially the
same in magnitude but opposite sign as that of 10. In
order to reconcile concerns about the influence of back-
ground dichroism from the remainder of the molecule,
the CD spectrum of pure penta-p-bromobenzoate 8
(28) We cannot, of course, rule out the very unlikely possibility of a
partial racemate containing ent-3 and, therefore, heterochirality in 1a -
g.
(29) Loss of the fatty acid side chain, e.g. 3, renders deacyl
bengazoles inactive against C. albicans.
(30) Hodges, J . C.; Patt, W. C.; Connolly, C. J . J . Org. Chem. 1991,
56, 449-452.

Synthesis of the Side Chain of Bengazoles C-G
J . Org. Chem., Vol. 61, No. 12, 1996 4077
547 (M + Na+, 6%), 525 (MH+, 38); HRFABMS found 525.3165
(MH+), C27H45N2O8 requires 525.3176.
of the synthesis of 1a and will report our findings in due
course.
Ben ga zole E (1e): UV (MeOH/H2O 9:1) λmax 217 nm; IR
(film) νmax 3600-3100, 2955, 2920, 2860, 1750, 1110 cm-1; 1H
NMR (CD3OD) δ 0.89 (t, J ) 7.0 Hz, 3H), 1.28 (m, 22H), all
other signals identical to those for bengazole A; 13C NMR (CD3-
OD) δ 14.4, 19.9, 23.7, 25.8, 30.0, 30.3, 30.5, 30.6, 30.7, 30.8
(4 × CH2), 33.1, 34.5, 40.4, 62.8, 66.2, 67.7, 71.2, 78.8, 127.5,
138.0, 145.6, 147.7, 154.4, 159.6, 173.3; FABMS m/ z 561 (M
+ Na+, 25%), 539 (MH+, 100); HRFABMS found 539.3326
(MH+), C28H47N2O8 requires 539.3332.
Ben ga zole F (1f): UV (MeOH/H2O 9:1) λmax 217 nm; IR
(film) νmax 3600-3100, 2955, 2925, 2855, 1750, 1110 cm-1; 1H
NMR (CD3OD) δ 0.88 (m, 6H), 1.28 (br s, 23H), all other signals
identical to those for bengazole A; FABMS m/ z 575 (M + Na+,
8%), 553 (MH+, 72); HRFABMS found 553.3481 (MH+),
C29H49N2O8 requires 553.3489.
Ben ga zole G (1g): UV (MeOH/H2O 9:1) λmax 217 nm; IR
(film) νmax 3600-3100, 2955, 2915, 2855, 1750, 1110 cm-1; 1H
NMR (CD3OD) δ 0.89 (t, J ) 7.0 Hz, 3H), 1.28 (m, 24H), all
other signals identical to those for bengazole A; FABMS m/ z
575 (M + Na+, 11%), 553 (MH+, 68); HRFABMS found
553.3481 (MH+), C29H49N2O8 requires 553.3489.
Meth a n olysis of Ben ga zoles. Samples (ca. 25 µg) of each
of 1a -g were dissolved in 5% HCl in MeOH (0.2 mL) and
heated at 50 °C for 2 h and treated as follows. The solution
was cooled, diluted with MeOH (1 mL), and extracted with
NaHCO3 (aqueous 7%) followed by n-hexane (3 × 1 mL). The
combined n-hexane extracts containing fatty acid methyl esters
(FAMEs) were dried (Na2SO4), and each sample was directly
analyzed by GCMS (0.25 mm × 25 m capillary, 150 °C, 5 min;
150-250 °C at 4 °C/ min, He carrier, quadrupole EIMS
detection). Eluted FAMEs were identified by single-ion moni-
toring of the prominent McLafferty rearrangement fragment
peak (M - 74) and matching of retention times with a standard
mixture of bacterial FAMEs (Supelco).
Exp er im en ta l Section
Gen er a l. Unless otherwise stated all new compounds were
purified to >95% as determined by NMR spectroscopy and
HPLC or TLC. Optical rotations were measured on a digital
spectropolarimeter. NMR spectra were recorded at 300 MHz
for 1H and 75.4 MHz for 13C. 1H and 13C NMR spectra are
referenced to residual CD3OD signals at 3.30 and 49.00 ppm,
CDCl3 at 7.26 and 77.00 ppm, or (CD3)2CO at 2.04 and 29.8
ppm, respectively. Mulitiplicities of 13C spectra were assigned
by DEPT experiments, and proton δ and J assignments were
aided by interpretation of COSY experiments. Standard pulse
sequences were employed for DEPT and magnitude COSY
experiments. IR spectra were recorded on a Fourier transform
instrument at 2 cm-1 resolution, and circular dichroism (CD)
measurements were made on a recording spectropolarimeter
interfaced to a microcomputer. UV spectra were recorded
using a diode array spectrophotomer or an analytical HPLC
with a diode array detector. Mass spectra were provided by
the University of Minnesota, Chemistry Department Mass
Spectrometry Service Laboratory. TLC was carried out on 0.2
mm silica gel plates impregnated with a fluorescent indicator
and visualized under a UV lamp or with 1% vanillin/EtOH/
H2SO4. All solvents were distilled in glass before use.
Collection a n d Extr a ction . The sponge J aspis sp. (90-
09-080) was collected in 1990 by hand using SCUBA at a depth
of 10 m on the Great Barrier Reef, Australia, and frozen at
-20 °C until required. Lyophilized animals (59.8 g) were
extracted with MeOH (350 mL), homogenized in MeOH (2 ×
500 mL), and filtered. The extracts were combined, concen-
trated to approximately 150 mL, and successively extracted
as follows. The water content (% v/v) of the MeOH extract
was adjusted prior to sequential partitioning against n-hexane
(10% v/v H2O), CCl4 (20% v/v H2O), and CHCl3 (40% v/v H2O).
Both the CCl4 (59.6 mg) and CHCl3 (111.3 mg) extracts
inhibited the growth of C. albicans and were combined. This
material was purified by flash chromatography (silica gel,
stepwise gradient elution CHCl3/MeOH 99:1 to 1:1). After the
elution of bengamides A and B,31 fractions eluting with CHCl3/
MeOH 90:10 and 80:20 were found to be antifungal and
exhibited sharp singlets due to oxazole and H10 protons in
their 1H NMR spectra at δ 7.0-9.0 suggestive of bengazoles.
These combined fractions were purified on reversed phase
cartridges (C18, MeOH/H2O 90:10) followed by HPLC (reversed
phase, C18, 5 µm, 300 × 10 mm, MeOH/H2O 90:10, 3 mL/min)
to afford the seven bengazoles A-G (1a -g, see Table 1).
Ben ga zole A (1a ): UV (MeOH/H2O 9:1) λmax 217 nm; CD
(MeOH) 202 nm (∆ꢀ +3.89), 217 (0), 231 (-1.55); 1H NMR
(CD3OD) and 13C NMR (CD3OD) identical with reported
values;13 FABMS m/ z 547 (M + Na+, 15%), 525 (MH+, 100);
HRFABMS found 525.3149 (MH+), C27H45N2O8 requires
525.3176.
Ben ga zole P en tol (3). A solution of mixed bengazoles
A-G (1a -g, 21.1 mg, obtained prior to HPLC, see isolation
procedure, above) in methanol (2.0 mL) was treated with a
saturated solution of ammonia in methanol (2.0 mL) and
stirred at 25 °C under a nitrogen atmosphere for 1.5 h. Solvent
was removed under reduced pressure, and the residue was
purified by column chromatography (silica gel, CHCl3/MeOH
4:1) to afford the pentol 3 as a colorless glass (12.1 mg, ca.
60%): [R]D +2.0° (c 0.76, MeOH); UV (MeOH) λmax 216 nm (ꢀ
9960); IR (film) νmax 3600-3100, 1105, 1065 cm-1 1H NMR
;
(CD3OD) δ 1.15 (d, J ) 6.5 Hz, 3H), 1.90 (ddd, J ) 14.0, 9.6,
6.9 Hz, 1H), 2.25 (ddd, J ) 14.0, 7.0, 2.7 Hz, 1H), 3.17 (dd, J
) 6.9, 3.2 Hz, 1H), 3.64 (ddd, J ) 9.6, 6.9, 2.7 Hz, 1H), 3.89
(qd, J ) 6.5, 3.2 Hz, 1H), 4.91 (dd, 7.0, 6.9 Hz, 1H), 5.98 (s,
1H), 7.17 (s, 1H), 7.82 (d, J ) 8.7 Hz, 2H), 8.20 (s, 1H); 13C
NMR (CD3OD) δ 19.9 (q), 40.6 (t), 62.9 (d), 66.3 (d), 67.7 (d),
71.2 (d), 78.7 (d), 125.1 (d), 137.5 (d), 145.2 (s), 151.7 (s), 153.7
(d), 163.3 (s); HRFABMS found 315.1196 (MH+), C13H19N2O7
requires 315.1192.
Ben ga zole A 2,3:4,6-Dia ceton id e (4). Bengazole A (1a ,
15.7 mg) was treated with 2,2-dimethoxypropane (2.0 mL) and
p-TSA (ca. 0.1 mg), and the solution was heated to 60 °C under
a nitrogen atmosphere for 1 h. Evaporation under reduced
pressure gave a yellow oil which was purified by column
chromatography (silica gel, CHCl3/MeOH 99:1) to afford the
diacetonide 4 as a colorless oil (14.5 mg, 80%): IR (film) νmax
1
Ben ga zole B (1b): UV (MeOH/H2O 9:1) λmax 217 nm; H
NMR (CD3OD) and 13C NMR (CD3OD) identical with reported
values;13 FABMS m/ z 561 (M + Na+, 15%), 539 (MH+, 100);
HRFABMS found 539.3305 (MH+), C28H47N2O8 requires
539.3332. This sample of bengazole B was obtained as an
inseparable 5/1 mixture of the iso and anteiso 15:0 fatty acid
esters as shown by GCMS.
1
1755 cm-1; H NMR (CDCl3) δ 0.87 (t, J ) 7.0 Hz, 3H), 1.24
Ben ga zole C (1c): UV (MeOH/H2O 9:1) λmax 217 nm; IR
(film) νmax 3600-3100, 2955, 2925, 2855, 1750, 1110 cm-1; 1H
NMR (CD3OD) δ 0.89 (t, J ) 7.0 Hz, 3H), 1.28 (m, 18H), all
other signals identical to those for bengazole A; FABMS m/ z
533 (M + Na+, 6%), 511 (MH+, 18); HRFABMS found 511.3019
(MH+), C26H43N2O8 requires 511.3019.
Ben ga zole D (1d ): UV (MeOH/H2O 9:1) λmax 217 nm; IR
(film) νmax 3600-3100, 2950, 2920, 2850, 1750, 1115 cm-1; 1H
NMR (CD3OD) δ 0.87 (d, J ) 6.6 Hz, 3H), 1.28 (m, 16H), all
other signals identical to those for bengazole B; FABMS m/ z
(m, 20H), 1.33 (d, J ) 6.2 Hz, 3H), 1.36 (s, 3H), 1.40 (s, 3H),
1.43 (s, 3H), 1.52 (s, 3H), 1.60 (m, 3H), 2.12 (dt, J ) 13.0, 2.5
Hz, 1H), 2.40 (t, J ) 7.6 Hz, 2H), 3.44 (t, J ) 7.3 Hz, 1H), 3.93
(ddd, J ) 11.4, 7.2, 2.4 Hz, 1H), 4.00 (dq, J ) 7.3, 6.2 Hz, 1H),
4.98 (dd, J ) 11.8, 2.3 Hz, 1H), 7.07 (s, 1H), 7.23 (s, 1H), 7.61
(s, 3H), 7.89 (s, 1H); FABMS 605 (MH+, 32%), 589 (M+ - CH3,
18), 547 (63), 531 (28); HRFABMS found 605.3817 (MH+),
C33H53N2O8 requires 605.3802.
10-Desa cylben ga zole 2,3:4,6-Dia ceton id e (5). A solution
of the diacetonide 4 (14.3 mg) in methanol (1.0 mL) was treated
with a saturated solution of ammonia in methanol (1.0 mL)
and stirred at 25 °C under a nitrogen atmosphere for 3 h.
Solvent was removed under reduced pressure, and the residue
(31) Quin˜oa`, E.; Adamczeski, M.; Crews, P.; Bakus, G. J . J . Org.
Chem. 1986, 51, 4494-4497.

4078 J . Org. Chem., Vol. 61, No. 12, 1996
Searle et al.
was purified by column chromatography (silica gel, CHCl3/
MeOH 99:1) to afford the C10 alcohol 5 as a colorless oil (8.1
mg, 87%): IR (film) νmax 3500-3100 cm-1; 1H NMR (CDCl3) δ
1.34 (d, J ) 6.1 Hz, 3H), 1.36 (s, 3H), 1.40 (s, 3H), 1.43 (s,
3H), 1.54 (s, 3H), 1.69 (ddd, J ) 13.0, 11.8, 11.4 Hz, 1H), 2.10
(ddd, J ) 13.0, 2.5, 2.1 Hz, 1H), 3.44 (dd, J ) 7.6, 7.2 Hz, 1H),
3.86 (br d, J ) 5.8 Hz, 1H), 3.94 (ddd, J ) 11.4, 7.2, 2.5 Hz,
1H), 4.00 (dq, J ) 7.6, 6.1 Hz, 1H), 4.97 (dd, J ) 11.8, 2.1 Hz,
1H), 5.98 (d, J ) 5.8 Hz, 1H), 7.13 (s, 1H), 7.60 (s, 1H), 7.88
(s, 1H); 13C NMR (CDCl3) δ 19.3 (q), 19.7 (q), 26.9 (q), 27.4 (q),
29.8 (q), 33.6 (t), 62.3 (d), 65.1 (d), 71.0 (d), 76.3 (d), 84.1 (d),
99.1 (s), 108.7 (s), 125.1 (d), 136.1 (d), 142.3 (s), 149.0 (s), 151.5
(d), 161.2 (s); FABMS m/z 395 (MH+, 58%), 379 (M+ - CH3,
10), 337 (45), 279 (100), 261 (30); HRFABMS found 395.1800
(MH+), C19H27N2O7 requires 395.1818.
as described previously.32 Purification of each crude product
by chromatography (basic alumina, 1:5 to 1:1 EtOAc/n-hexane)
gave (R)-MTPA ester 9a (65%) and (S)-MTPA ester 9b (46%,
see Figure 2 for 1H NMR ∆δ18). Ester 9a : HRFABMS found
(MH+) 611.2214, calculated for C29H33N2O9F3 611.2216. Ester
9b : HRFABMS found (MH+) 611.2229, calculated for
C29H33N2O9F3 611.2216.
Ben ga zole Tetr a -p-bromobenzoate (10). The mixture of
bengazoles A-G (1a-g, 2.0 mg) was converted to their
corresponding tetra-O-p-bromobenzoates as described above
for 8. Purification of the crude product by chromatography
(silica gel, 75:25 n-hexane/EtOAc) gave tetra-O-p-bromoben-
zoate 10 as a mixture of fatty acid esters at O-C10 (1.2 mg,
∼25%) and as a colorless glass: CD (MeCN) 252 (∆ꢀ -14.6),
246 (0), 235 (+17.4), 219 (+3.2), 208 (12.8), 200 (0), 197 (-9.8).
(1R,3S,4R,5R)1-P h en ylh exa n e-1,3,4,5-tetr ol Tetr a -O-p-
br om oben zoa te (11). A solution of the tetrol 2 (5.0 mg, 0.022
mmol) in pyridine (3 mL) was treated with p-bromobenzoyl
chloride (80 mg, 0.36 mmol) and 4-(N,N-dimethylamino)-
pyridine (ca. 0.1 mg). After 18 h of stirring at 25 °C, 3-(N,N-
dimethylamino)propylamine (800 µL) was added and stirring
continued for a further 30 min. Pyridine was removed under
high vacuum, and the residue was chromatographed on silica
gel (hexane/EtOAc 9:1) to afford the tetra-p-bromobenzoate 11
as a colorless glass (19.2 mg, 91%): UV (MeCN) λmax 244 nm
(ꢀ 70100); CD (MeCN) λ 252 (∆ꢀ +6.5), 244 (0), 234 (-19.5),
207 (-9.8), 200 (0), 197 (+2.5); IR (film) νmax 1710, 1590, 1266,
1099, 1011, 753 cm-1; 1H NMR (CDCl3) δ 1.28 (d, J ) 6.5 Hz,
3H), 2.42 (ddd, J ) 14.6, 7.4, 2.6 Hz, 1H), 2.71 (ddd, J ) 14.6,
9.6, 6.4 Hz, 1H), 5.43 (m, 2H), 5.62 (dd, J ) 5.3, 4.8 Hz, 1H),
6.09 (dd, J ) 7.4, 6.4 Hz, 1H), 7.24-7.34 (m, 5H), 7.46 (d, J )
8.5 Hz, 2H), 7.47 (d, J ) 8.5 Hz, 2H), 7.48 (d, J ) 8.5 Hz, 2H),
7.58 (d, J ) 8.5 Hz, 2H), 7.65 (d, J ) 8.5 Hz, 2H), 7.71 (d, J )
8.5 Hz, 2H), 7.79 (d, J ) 8.5 Hz, 2H), 7.84 (d, J ) 8.5 Hz, 2H);
HRFABMS found 954.8815 (MH+), C40H31O8Br4 requires
954.8752.
Ben zyl L-F u cop yr a n osid e (12) a n d Ben zyl 3,4-Isop r o-
p ylid en e-L-fu cop yr a n osid e (13). A stirred suspension of
L-fucose (2.00 g, 12.2 mmol) in benzyl alcohol (10 mL) was
saturated with dry HCl gas (∼10 min), stirred for 3 h at 25
°C, and then allowed to stand at 4 °C for 16 h. The volatiles
were removed under vacuum, and the residue was purified
by column chromatography (silica gel, MeOH/CHCl3 1:19 to
1:9) to provide pure 1-O-benzyl-L-fucose (12, 2.48 g, 80%) as a
viscous oil (5/1 mixture of â/R anomers, by 1H NMR) which
was used directly in the next step. Benzyl glycoside 12 was
suspended in acetone (20 mL) and 2,2-dimethoxypropane (30
mL) and stirred with a catalytic amount of p-TSA. The
mixture produced a homogeneous solution after 15 min. After
1.5 h, the mixture was concentrated and the residue was
purified by chromatography (silica gel, ethyl acetate/hexane
1:1 ) to give 1-O-benzyl acetonide 13 as a viscous colorless oil
(2.78, 97%) that was used directly in the next step.
Ben ga zole Aceton id e 10-O-p-Br om oben zoa te (6).
A
solution of 5 (7.9 mg) in pyridine (1.5 mL) was treated with
p-bromobenzoyl chloride (100 µL) and DMAP (ca. 0.1 mg), and
the solution was heated at 50 °C for 2 h. Pyridine was
removed under high vacuum, and the residue was purified by
preparative TLC (silica gel, 1 mm, CHCl3/MeOH 96.5:3.5) to
afford the p-bromobenzoyl derivative 6 as a colorless solid (8.2
1
mg, 71%): IR (film) νmax 1735 cm-1; H NMR (CDCl3) δ 1.33
(d, J ) 6.0 Hz, 3H), 1.36 (s, 3H), 1.40 (s, 3H), 1.43 (s, 3H),
1.53 (s, 3H), 1.65 (ddd, J ) 13.0, 11.4, 11.3 Hz, 1H), 2.13 (dt,
J ) 13.0, 2.5 Hz, 1H), 3.44 (t, J ) 7.4 Hz, 1H), 3.94 (ddd, J )
11.4, 7.1, 2.5 Hz, 1H), 4.00 (dq, 7.4, 6.0 Hz, 1H), 4.99 (dd, J )
11.3, 2.5 Hz, 1H), 7.30 (s, 1H), 7.32 (s, 1H), 7.60 (d, J ) 8.7
Hz, 2H), 7.65 (s, 1H), 7.93 (d, J ) 8.7 Hz, 2H), 7.93 (s, 1H);
FABMS m/ z 579 (MH+ + 2, 14%), 577 (MH+, 13), 521 (18),
519 (20), 463 (30), 461 (32), 185 (95), 183 (100); HRFABMS
found 577.1188 (MH+), C26H30N2O8Br requires 577.1186.
Ben ga zole Tetr ol 10-O-p-Br om oben zoa te (7). A solu-
tion of 6 in THF (1.0 mL) was treated with 50% aqueous acetic
acid (1.6 mL) and heated to 60 °C under a nitrogen atmosphere
for 19 h. The solution was evaporated to dryness under
reduced pressure, and the residue was purified by column
chromatography (silica gel, CHCl3/MeOH 9:1) to afford the
p-bromobenzoyl derivative 7 as a colorless solid (3.6 mg,
69%): IR (film) νmax 3600-3100, 1730 cm-1 1H NMR (CD3-
;
OD) δ 1.11 (d, J ) 6.6 Hz, 3H), 1.90 (ddd, J ) 14.0, 9.7, 6.8
Hz, 1H), 2.23 (ddd, J ) 14.0, 7.2, 2.7 Hz, 1H), 3.16 (dd, J )
6.7, 3.4 Hz, 1H), 3.65 (ddd, J ) 9.7, 6.7, 2.7 Hz, 1H), 3.89 (qd,
J ) 6.6, 3.4 Hz, 1H), 4.92 (dd, 7.2, 6.8 Hz, 1H), 7.35 (s, 1H),
7.41 (s, 1H), 7.69 (d, J ) 8.7 Hz, 2H), 7.88 (s, 1H), 7.95 (d, J
) 8.7 Hz, 2H), 8.29 (s, 1H); FABMS m/ z 499 (MH+ + 2, 41%),
497 (MH+, 42); HRFABMS found 497.0560 (MH+), C20H22N2O8-
Br requires 497.0559.
Ben ga zole P en ta -p-br om oben zoa te (8). A solution of 3
(5.3 mg) in pyridine (2.0 mL) was treated with p-bromobenzoyl
chloride (ca. 16 mg) and DMAP (ca. 0.1 mg), and the solution
was heated at 55 °C for 20 h. Excess p-bromobenzoyl chloride
was quenched by the addition of 3-(N,N-dimethylamino)-
propylamine (50 µL), and the reaction mixture was stirred for
an additional 1 h. Pyridine was removed under high vacuum,
and the residue was purified by column chromatography (silica
gel, CHCl3/MeOH 0.5%) to afford the penta-p-bromobenzoate
8 as a colorless solid (18.5 mg, 89%): CD (CH3CN) 252 nm
(∆ꢀ -2.7), 246 (0), 236 (+10.2), 208 (+8.7), 200 (0), 198 (-0.2);
Ben zyl 2-Deoxy-3,4-isop r op ylid en e-L-fu cop yr a n osid e
(15). (i) A solution of the fucose derivative 13 (2.90 g, 9.85
mmol) in THF (20 mL) was added to a dispension of sodium
hydride (0.59 g, 80% dispersion, 19.7 mmol) in THF (10 mL).
Imidazole (20 mg) was added, and the mixture was stirred at
25 °C under nitrogen. After 30 min, carbon disulfide (4.5 mL,
75 mmol) was added and stirring continued (1 h). Methyl
iodide (1.5 mL, 24 mmol) was then added, and after a further
15 min of stirring, the reaction mixture was poured into water
(100 mL) and extracted with CH2Cl2 (3 × 100 mL). The
combined, dried (MgSO4) extracts were evaporated under
reduced pressure to give the crude xanthate 14 (3.72 g, 98%),
which was used directly in the next step.
(ii) The xanthate 14 (3.72 g, 9.69 mmol) was dissolved in
dioxane (40 mL), triethylamine (14.9 mL, 107 mmol), and 50%
aqueous hypophosphorous acid (5.0 mL, 48 mmol) under
nitrogen. A 1 mL aliquot of a solution of AIBN (0.79 g, 4.84
mmol, in 5 mL dioxane) was added, and the reaction mixture
was heated to reflux. Further 1 mL aliquots of AIBN solution
were added until the reaction was complete by TLC (2.5 h).
IR (film) νmax 1710, 1580, 1245, 1075, 1065, 1005, 745 cm-1
;
1H NMR (CDCl3) δ 1.36 (d, J ) 6.4 Hz, 3H), 2.75 (m, 2H), 5.45
(m, 1H), 5.50 (qd, J ) 6.4, 6.2 Hz, 1H), 5.63 (dd, J ) 6.2, 4.2
Hz, 1H), 6.13 (dd, J ) 7.8, 6.1 Hz, 1H), 7.25 (s, 1H), 7.32 (s,
1H), 7.44 (d, J ) 8.6 Hz, 2H), 7.47 (d, J ) 8.6 Hz, 2H), 7.49 (d,
J ) 8.6 Hz, 2H), 7.55 (d, J ) 8.6 Hz, 2H), 7.59 (d, J ) 8.6 Hz,
2H), 7.65 (d, J ) 8.6 Hz, 2H), 7.68 (s, 1H), 7.72 (d, J ) 8.6 Hz,
2H), 7.78 (d, J ) 8.6 Hz, 2H), 7.82 (d, J ) 8.6 Hz, 2H), 7.91 (d,
J ) 8.6 Hz, 2H); FABMS m/ z 1224.8 (MH+, 5%) 1024.8 (M+
-
C7H4BrO2, 77%); HRFABMS found 1224.8010 (MH+),
C48H34N2O12Br5 requires 1224.8029.
(R)- a n d (S)-MTP A Mosh er Ester s 9a a n d 9b . Samples
of alcohol 6 (ca. 1-2 mg) were acylated, separately, with (R)-
and (S)-MTPA in the presence of DCC and DMAP in CH2Cl2
(32) Searle, P. A.; Molinski, T. F. Tetrahedron 1994, 50, 9893-9908.

Synthesis of the Side Chain of Bengazoles C-G
J . Org. Chem., Vol. 61, No. 12, 1996 4079
The reaction mixture was poured into water and extracted
with CH2Cl2 (3 × 100 mL). The combined extracts were dried
(MgSO4) and evaporated under reduced pressure to give a
yellow oil. Purification by column chromatography on silica
gel (hexane/EtOAc 9:1 to 7:3) gave the 2-deoxy compound 15
as a mixture of anomers (1.99 g, 74%), together with recovered
starting material 14 (20%). A portion of the product was
separated by preparative HPLC (Microsorb silica gel, hexane/
EtOAc 8:2) to afford pure anomers, in order of elution, 15â
and 15R.
25.4 (q), 27.8 (q), 39.0 (t), 65.4 (d), 73.8 (d), 76.6 (d), 81.7 (d),
108.7 (s), 125.9 (2 × d), 127.6 (d), 128.4 (2 × d), 143.8 (s);
HRCIMS found 284.1875 (M + NH4+), C15H26NO4 requires
284.1862. Min or d ia ster eom er (17b): 1H NMR (CDCl3) δ
1.15 (d, J ) 6.2 Hz, 3H), 1.38 (s, 3H), 1.53 (s, 3H), 3.77 (m,
1H), 3.86 (m, 1H), 4.42 (ddd, J ) 11.3, 6.0, 2.4 Hz, 1H), 4.98
(dd, J ) 9.0, 3.2, Hz, 1H), 7.23-7.40 (m, 5H).
(1R,3S,4R,5R)-1-P h en ylh exa n -1,3,4,5-tetr ol (2). A solu-
tion of the acetonide 17a (28.6 mg, 0.107 mmol) in 50%
aqueous THF (8 mL) was stirred with Dowex 50-X8 (H+) ion-
exchange resin. After 18 h, the resin was removed by filtration
and washed with THF (5 mL) and water (1 mL). The combined
filtrates were evaporated under reduced pressure, and the
residue was chromatographed on a short column of silica gel
(EtOAc) to afford the tetrol 2 as a colorless amorphous solid
(20.6 mg, 85%), mp 85-87 °C (benzene): [R]D +3.2° (c 1.0,
MeOH); UV (MeOH) λmax 207 nm (ꢀ 8500); IR (film) νmax 3500-
3100 (br), 1062, 1005, 990, 698 cm-1; 1H NMR (CD3OD) δ 1.10
(d, J ) 6.5 Hz, 3H), 1.90 (ddd, J ) 14.0, 9.7, 7.2 Hz, 1H), 2.06
(ddd, J ) 14.0, 6.9, 2.6 Hz, 1H), 3.13 (dd, J ) 6.9, 6.2 Hz, 1H),
3.57 (ddd, J ) 9.7, 6.9, 2.6 Hz, 1H), 3.90 (qd, J ) 6.5, 3.2 Hz,
1H), 4.90 (dd, J ) 7.2, 6.9 Hz, 1H), 7.20-7.40 (m, 5H); 13C
NMR (CD3OD) δ 19.8 (q), 43.2 (t), 67.6 (d), 71.6 (d), 74.1 (d),
78.8 (d), 127.4 (2 × d), 128.4 (d), 129.3 (2 × d), 146.0 (s);
HRCIMS found 244.1554 (M + NH4+), C12H22NO4 requires
244.1549. Anal. Calcd for C12H18O2: C, 63.70; H 8.02.
Found: C, 63.55; H, 7.99.
(+)-1r-Ben zyl-2-d eoxy-3,4-isop r op ylid en e-L-fu cop yr a -
n ose (15â): glass, [R]D +46.3° (c 1.0, CHCl3); IR (film) νmax
2984, 2937, 2871, 1380, 1368, 1244, 1218, 1085, 1027 cm-1
;
1H NMR (CDCl3) δ 1.27 (d, J ) 6.5 Hz, 1H), 1.34 (s, 3H), 1.49
(s, 3H), 1.80 (ddd, J ) 14.9, 6.3, 3.9 Hz, 1H), 2.22 (ddd, J )
14.9, 5.1, 5.1 Hz, 1H), 3.92 (qd, J ) 6.5, 2.0 Hz, 1H), 3.99 (dd,
J ) 7.1, 2.0 Hz), 4.48 (m, 1H), 4.51 (d, J ) 12.0 Hz, 1H), 4.78
(d, J ) 12.0 Hz, 1H), 5.03 (dd, J ) 6.3, 5.1 Hz, 1H), 7.25-7.35
(m, 5H); 13C NMR (CDCl3) δ 16.0 (q), 25.4 (q), 26.8 (q), 30.7
(t), 64.7 (d), 69.1 (t), 70.8 (d), 75.4 (d), 95.9 (d), 108.7 (s), 127.4
(d), 127.7 (2 × d), 128.3 (2 × d), 138.5 (s); HRCIMS found
279.1586 (MH+), C16H23O4 requires 279.1596.
(-)-1â-O-Ben zyl-2-d eoxy-3,4-isop r op ylid en e-L-fu cop y-
r a n ose (15r): solid, [R]D -80.3° (c 1.0, CHCl3); IR (film) νmax
2983, 2935, 2902, 1379, 1360, 1215, 1124, 1063, 1041, 1027,
1
1020 cm-1; H NMR (CDCl3) δ 1.33 (s, 3H), 1.45 (d, J ) 6.6
Hz, 3H), 1.52 (s, 3H), 1.70 (ddd, J ) 12.8, 9.8, 9.8 Hz, 1H),
2.09 (ddd, J ) 12.9, 7.0, 2.0 Hz, 1H), 3.75 (qd, J ) 6.6, 2.1 Hz,
1H), 3.83 (dd, J ) 5.1, 2.1 Hz, 1H), 4.22 (ddd, J ) 9.8, 7.0, 5.2
Hz, 1H), 4.39 (dd, J ) 9.8, 2.0 Hz, 1H), 4.58 (d, J ) 12.0 Hz,
1H), 4.91 (d, J ) 12.0 Hz, 1H), 7.25-7.36 (m, 5H); 13C NMR
(CDCl3) δ 16.9 (q), 26.4 (q), 28.3 (q), 35.5 (t), 69.1 (d), 70.0 (t),
72.6 (d), 74.3 (d), 98.3 (d), 109.2 (s), 127.6 (d), 128.0 (2 × d),
128.3 (2 × d), 137.9 (s); HRCIMS found 279.1586 (MH+),
C16H23O4 requires 279.1596.
(1R,3S,4R,5R)-1-P h en yl-1,3:4,5-O-d iisop r op ylid en eh ex-
a n e-1,3,4,5-tetr ol (18). A solution of the tetrol 2 (4.9 mg,
0.022 mmol) in acetone (1 mL) was treated with 2,2-dimethox-
ypropane (1 mL) and p-TSA (ca. 0.1 mg). After 3 h of stirring
at 25 °C, the reaction mixture was evaporated to dryness and
the residue purified by flash chromatography (silica gel,
hexane/EtOAc 1:1) to afford the diacetonide 18 as a colorless
glass (4.9 mg, 74%): [R]D +3.0° (c 0.33, MeOH); UV (MeOH)
λmax 207 nm (ꢀ 8500); IR (film) νmax 2989, 1379, 1200, 1168,
2-Deoxy-3,4-isop r op ylid en e-L-fu cose (16). A solution of
benzyl glycoside 15 (1.76 g, 6.32 mmol) in absolute EtOH (25
mL) was treated with Pearlman’s catalyst (1.0 g) and stirred
under a hydrogen atmosphere for 2 days. The suspension was
then filtered through a short pad of diatomaceous earth, the
pad was washed with EtOH, and the combined EtOH solutions
were evaporated to give a yellow oil. Purification by column
chromatography on silica gel (CHCl3/MeOH 95:5) afforded the
debenzylated product 16 as a mixture of anomers (0.92g, 77%)
that was used immediately in the next step.
1
1103, 1066, 854, 699 cm-1; H NMR (acetone-d6) δ 1.28 (d, J
) 6.0 Hz, 3H), 1.29 (s, 3H), 1.30 (s, 3H), 1.40 (s, 3H), 1.45 (ddd,
J ) 12.9, 11.5, 11.5 Hz, 1H, H2â), 1.56 (s, 3H), 1.96 (ddd, J )
12.9, 2.5, 2.5 Hz, 1H, H2R), 3.37 (dd, J ) 7.7, 7.0 Hz, 1H, H4),
3.99 (dq, J ) 7.7, 6.0 Hz, 1H, H5), 4.08 (ddd, J ) 11.5, 7.0, 2.5
Hz, 1H, H3), 5.04 (dd, J ) 11.5, 2.5 Hz, 1H, H1), 7.21-7.42
(m, 5H); 13C NMR (acetone-d6) δ 19.5 (q), 20.1 (q), 27.2 (q),
27.7 (q), 30.4 (q), 37.5 (t), 71.4 (d), 71.9 (d), 76.7 (d), 85.1 (d),
99.4 (s), 108.9 (s), 126.6 (2 × d), 128.0 (d), 129.0 (2 × d), 143.8
(s); HRCIMS (NH3) found 249.1486 (MH+ - C3H60), C18H26O4
requires 249.1491.
(1R,3S,4R,5R)-1-P h en yl-3,4-O-isop r op ylid en eh exa n e-
1,3,4,5-tetr ol (17a ) a n d (1S,3S,4R,5R) Isom er (17b). Phe-
nyllithium (1.8 M solution in cyclohexane/diethyl ether, 6.0
mL, 10.8 mmol) was added slowly to a stirred solution of the
sugar derivative 16 (406 mg, 2.16 mmol) in THF (10 mL) at
-78 °C under nitrogen. The reaction mixture was stirred for
1 h at -78 °C and then at 0 °C for 2 h. A saturated ammonium
chloride solution (10 mL) was added, and the reaction mixture
was diluted with water (50 mL) and extracted with CH2Cl2 (3
× 100 mL). The combined organic extracts were dried (MgSO4)
and evaporated under reduced pressure to give a yellow oil.
Purification by flash chromatography on silica gel (hexane/
EtOAc 1:1) afforded a mixture of acetonides 17a and 17b as a
colorless glass (496 mg, 86%). The 1H NMR spectrum indi-
cated a 2.4:1 ratio of 17a :17b. An analytically pure sample
of the major diastereomer was obtained by preparative HPLC
(Microsorb silica gel, hexane/EtOAc 1:1), while the minor
compound 17b could only be obtained as an enriched mixture
with 17a (∼60% purity).
Ack n ow led gm en t. This research was supported by
the NIH (AI-31660) and the UC Davis Committee on
Research. We thank Dr. Dan J ones (University of
California, Davis, Facility for Advanced Instrumenta-
tion) for assistance with the GCMS analysis, Mary Kay
Harper (Scripps Institution of Oceanography) for taxo-
nomic identification of the sponge, Dr. Ed Larka (Uni-
versity of Minnesota) for the high-resolution mass
spectra, and Professor Barry Trost (Stanford) for useful
comments regarding determination of C10 configuration
in 1a . T.F.M. gratefully acknowledges the receipt of an
American Cyanamid Faculty Award.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
1-11, 15 (R and â epimers), 17a -b and 18, 13C NMR spectra
of 1e, 3, and 17a , and CD spectra of 1a and 8 (29 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
Ma jor d ia ster eom er (17a ): [R]D -45.0° (c 1.0, MeOH); UV
(MeOH) λmax 207 nm (ꢀ 8310); IR (film) νmax 3450 (br), 2984,
1
1380, 1371, 1238, 1219, 1060, 702 cm-1; H NMR (CDCl3) δ
1.13 (d, J ) 6.2 Hz, 3H), 1.38 (s, 3H), 1.56 (s, 3H), 1.75 (ddd,
J ) 13.9, 4.5, 2.4 Hz, 1H), 2.12 (ddd, J ) 13.9, 11.3, 8.5 Hz,
1H), 3.75 (qd, J ) 6.2, 6.2 Hz, 1H), 3.85 (dd, J ) 6.2, 6.0 Hz,
1H), 4.23 (ddd, J ) 11.3, 6.0, 2.4 Hz, 1H), 4.90 (dd, J ) 8.5,
4.5 Hz, 1H), 7.23-7.40 (m, 5H); 13C NMR (CDCl3) δ 19.7 (q),
J O952261A