Structure and total synthesis of HF-7, a neuroactive glyconucleoside disulfate from the funnel-web spider Hololena curta

Article abstract of DOI:10.1021/ja990274q

Spider venom toxins have attracted considerable attention for their ability to block the action of excitatory amino acids such as glutamate and aspartate. A new neuroactive compound designated HF-7 was isolated in 1993 from the venom of a funnel-web spide

Full text of DOI:10.1021/ja990274q

J. Am. Chem. Soc. 1999, 121, 5661-5665
5661
Structure and Total Synthesis of HF-7, a Neuroactive Glyconucleoside
Disulfate from the Funnel-Web Spider Hololena curta
Jinping McCormick,† Yingbo Li,† Kevin McCormick,† Howard I. Duynstee,‡
Anke K. van Engen,‡ Gijs A. van der Marel,‡ Bruce Ganem,† Jacques H. van Boom,‡ and
Jerrold Meinwald*,†
Contribution from the Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell
UniVersity, Ithaca, New York 14853-1301, and Leiden Institute of Chemistry, Gorlaeus Laboratories,
Leiden UniVersity, P.O. Box 9502, 2300 RA Leiden, The Netherlands
ReceiVed January 27, 1999
Abstract: Spider venom toxins have attracted considerable attention for their ability to block the action of
excitatory amino acids such as glutamate and aspartate. A new neuroactive compound designated HF-7 was
isolated in 1993 from the venom of a funnel-web spider, Hololena curta. HF-7 was shown to block kainate
receptors and, albeit weakly, L-type calcium channels. Spectroscopic analysis established the structure of HF-7
as an unusual acetylated, disulfated fucopyranosyl guanosine, with the acetate ester attached at the 4-position
of an R-linked fucose ring and two sulfates attached to the ribose ring. Because insufficient quantities of
natural HF-7 were available for chemical degradation or X-ray diffraction analysis, total synthesis of three
candidate structures was used to establish the identity of HF-7. Once HF-7 was fully characterized as 3′-O-
(4′′-O-acetyl-R-L-fucopyranosyl)guanosine-2′,5′-disulfate, an improved, targeted synthesis of the natural product
was developed.
The remarkable dominance of insects and other arthropods
on land can be attributed, in part, to the extraordinary diversity
of their chemical defense mechanisms.1 In addition to glandular
defensive secretions and systemic antifeedants, some anthropods
muster offensive chemical weaponry to capture their prey. In
this regard, spider venom toxins have attracted considerable
attention for their ability to block the action of excitatory amino
acids such as glutamate and aspartate.2 Receptors for such amino
acids (NMDA, kainate, quisqualate/AMPA) and their closely
associated ion channels affect the intracellular concentration of
Ca2+ in nerve cells and are important in a variety of neural
functions, including pain,3 motor control,4 learning, and memory.5
Most spider-derived toxins are characterized by polypeptide,
protein, or polyamine backbones.6 As part of a collaboration
between scientists at Cornell University and Cambridge Neu-
roScience, Inc., a new neuroactive compound designated HF-7
was isolated in 1993 from the venom of a funnel-web spider,
Hololena curta.7 This highly polar agent was shown to block
kainate receptors and, albeit weakly, L-type calcium channels.
Such agents might be used in treating global cerebral ischemia,
a form of excitotoxicity mediated by non-NMDA receptors that
can arise following cardiac arrest, drowning, or carbon monoxide
poisoning.8
From initial spectroscopic analysis, it was clear that HF-7
belonged to no known class of spider venoms. The presence of
a guanine chromophore was established by ultraviolet absorption
spectroscopy. Satisfactory mass spectrometric data could only
be obtained by negative ion fast atom bombardment (FAB) mass
spectrometry, which revealed a parent monoanion at m/z 630
corresponding to a molecular weight of 631 Da. The presence
of a sulfate group was confirmed by loss of an 80 Da fragment
from this anion, corresponding to the loss of SO3 from the parent
ion. Exact mass measurement of the resulting base peak in the
spectrum established the molecular formula C18H24N5O13S (m/z
obsd 550.1036; calcd 550.1091), from which the molecular
formula for HF-7 was inferred to be C18H24N5O16S2. Further
spectroscopic analysis established the structure of HF-7 as an
unusual acetylated, disulfated fucopyranosyl guanosine, with the
acetate ester attached at the 4-position of an R-linked fucose
ring and two sulfates attached to the ribose ring.
Several aspects of the overall structure of HF-7 are notewor-
thy. To our knowledge, HF-7 is, together with liposidomycin,9
the only known naturally occurring sulfated nucleosides. Related
anionic nucleosides include 3′-phospho-adenosine-5′-phospho-
sulfate and the sulfamoylated nucleosides ascamycin,10 AT-
265,11 and nucleocidin.12 HF-7 also belongs to a very small
† Cornell University.
‡ Leiden University.
(1) Meinwald, J.; Eisner, T. Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 14-
18.
(2) McLennan, H. Excitatory Amino Acid Transmission; A. R. Liss: New
York, 1988; pp 1-18.
(3) Jacquet, Y. F. Eur. J. Pharmocol. 1988, 154, 271.
(4) Cavalheiro, E. A.; Lehmann, J.; Turski, L. Frontiers on Excitatory
Amino Acid Research; A. R. Liss: New York, 1988.
(5) Bliss, T. V. P.; Collingridge, G. L. Nature 1993, 361, 31-39.
(6) (a) McCormick, K. D.; Meinwald, J. J. Chem. Ecol. 1993, 19, 2411-
2450. (b) Schulz, S. Angew. Chem., Int. Ed. Engl. 1997, 36, 314-326.
(7) (a) McCormick, K. D. Ph.D. Dissertation, Cornell University, Ithaca,
NY, 1993. (b) Goldin, S.; Fisher, J.; Kobayashi, K.; Reddy, L.; Knapp,
A.; Margolin, L.; McCormick, K. D. Fucosylated Guanosine Disulfates as
Excitatory Amino Acid Antagonists. U.S. Patent No. 5,438,130, issued
August 1, 1995.
(8) Busto, R.; Globus, M. Y. T.; Dietrich, W. D.; Martinez, E.; Valdes,
I.; Ginsberg, M. D. Stroke 1989, 20, 904-910.
(9) (a) Isono, K.; Uramoto, M.; Kusakabe, H.; Kimura, K.; Izaki, K.;
Nelson, C. C.; McCloskey, J. A. J. Antibiot. 1985, 38, 1617. (b) Ubukata,
M.; Isono, K. J. Am. Chem. Soc. 1988, 110, 4416.
(10) Isono, K.; Uramoto, M.; Kusakabe, H.; Miyata, N.; Koyama, T.;
Ubukata, M.; Sethi, K. K.; McCloskey, J. A. J. Antibiot. 1984, 37, 670-
672.
(11) Takahashi, E.; Beppu, T. J. Antibiot. 1982, 35, 939-947.
10.1021/ja990274q CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/06/1999

5662 J. Am. Chem. Soc., Vol. 121, No. 24, 1999
McCormick et al.
Scheme 1
Scheme 2a
a Conditions: (a) Bu2SnO, toluene, reflux, 16 h; (b) BnBr, DMF,
90 °C, 9 h; (c) Ac2O, pyr, room temperature, 16 h; (d) (Ph3P)3RhCl,
EtOH, reflux, 22 h; (e) HgO, HgCl2, 9:1 acetone/H2O, room temper-
ature, 2 h; (f) carbonyldiimidazole, ether, room temperature, 1 h.
for further biological evaluation. To establish the structure of
HF-7, we herein report the synthesis of four acetylated,
disulfated fucosylguanosines: 2′-O-(4′′-O-acetyl-R-L-fucopy-
ranosyl)guanosine-3′,5′-disulfate (1), 3′-O-(4′′-O-acetyl-R-L-
fucopyranosyl)guanosine-2′,5′-disulfate (2), 5′-O-(4′′-O-acetyl-
R-L-fucopyranosyl)guanosine-2′,3′-disulfate (3), and 3′-O-(4′′-
O-acetyl-R-D-fucopyranosyl)guanosine-2′,5′-disulfate (4). On the
basis of spectroscopic comparisons with the natural product,
the structure of HF-7 was shown to be (-)-2 (Scheme 1).
Following preliminary disclosure of the isolation and charac-
terization of HF-7,1 an efficient route specifically designed for
the regio- and stereoselective synthesis of (-)-2 itself was
developed.
One synthetic approach to regioisomers 1-3 relied on
coupling guanosine derivatives suitably blocked at the 2′-, 3′-,
or 5′-positions with an acetylated and appropriately protected
fucopyranosyl donor. Several multistep procedures for distin-
guishing the hydroxyl groups of L-fucose have been developed
in synthetic studies on blood-group determinants.16 Guided
ultimately by the requisite compatibility (and selective cleavage)
of protecting groups in the two saccharide subunits, we imple-
mented an expeditious route to 4-O-acetyl-2,3-di-O-benzyl-1-
O-imidazolylcarbonyl-R-L-fucopyranoside (8), depicted in Scheme
2. Reactions of the known allyl R-L-fucopyranoside (5)17 with
2 equiv of Bu2SnO in toluene, followed by heating with excess
BnBr in DMF, afforded 2,3-dibenzyl ether 6 in 68% yield. A
similar, tin-mediated 2,3-di-O-benzylation of methyl R-D-
galactopyranoside (13% yield) was recently reported.18 The
mechanism of this reaction, although unknown, was suggested
to involve initial benzylation at O2, followed by benzylation at
O3. Acetylation of 6 afforded 7, which, upon subsequent
deallylation using Wilkinson’s catalyst followed by HgCl2/HgO,
afforded 8. Compound 8 was transformed into imidazolylcar-
bonyl glycoside 9. We chose this type of glycosylating agent
on the basis of its successful use in the synthesis of avermectin
by Ley and Ford,19 who found that it worked well in the
construction of a hindered glycoside, and that it strongly favored
R-glycosylation.
family of glycosylated nucleosides13 and contains the more
unusual R-glycosidic linkage. Other known examples are the
fucosylated nucleoside shimofuridins A-G14 and the phospho-
rylated nucleoside glycosides adenophostin A and B, which also
affect Ca2+ release.15
Limited amounts of natural HF-7 available precluded the use
1
of H-detected (1H, 13C) multiple bond correlation (HMBC)
NMR spectroscopy to identify the site of the fucose linkage,
and hence the sites of sulfation on the ribose ring. With
insufficient quantities for chemical degradation or X-ray dif-
fraction analysis, the absolute configuration of the fucose and
ribose could not be determined. Since a D- or L-fucose could
be joined at the 2′-, 3′-, or 5′-positions of a D- or L-ribose, 12
candidates were possible for the structure of HF-7. Assuming
utilization of the more common enantiomers of monosaccharides
(D-ribose and L-fucose), the number of possibilities was reduced
to three (1-3, Scheme 1).
In such a situation, total synthesis of the candidate structures
represents a useful way to complete the characterization of a
new natural product, as well as to obtain adequate quantities of
both the natural material and some closely related analogues
(12) (a) Waller, C. W.; Patrick, J. B.; Fulmor, W.; Merey, W. E. J. Am.
Chem. Soc. 1957, 79, 1011-1012. (b) Morton, G. O.; Lancaster, J. E.; Van
Lear, G. E.; Meyer, W. E. J. Am. Chem. Soc. 1969, 91, 1535-1537.
(13) For other glycosylated nucleosides, see: Knapp, S. Chem. ReV. 1995,
95, 1859-1876.
(14) (a) Kobayashi, J.; Doi, Y.; Ishibashi, M. J. Org. Chem. 1994, 59,
255. (b) Doi, Y.; Ishibashi, M.; Kobayashi, J. Tetrahedron 1994, 50, 8651.
(c) Duynstee, H. I.; Wijsman, E. R.; van der Marel, G. A.; van Boom, J. H.
SynLett 1996, 313-314. (d) Knapp, S.; Gore, V. K. J. Org. Chem. 1996,
61, 6744-6747.
Scheme 3 depicts the synthesis of appropriate guanosine
building blocks 12 and 13 used to prepare target structures 1-4.
(15) (a) Takahashi, M.; Tanzawa, K.; Takahashi, S. J. Biol. Chem. 1994,
269, 369-372. (b) Hotoda, H.; Takahashi, M.; Tanzawa, K.; Takahashi,
S.; Kaneko, M. Tetrahedron Lett. 1995, 36, 5057-5040. (c) Jenkins, D. J.;
Potter, B. V. L. Carbohydr. Res. 1996, 287, 169-182. (d) van Straten, N.
C. R.; van der Marel, G. A.; van Boom, J. H. Tetrahedron 1997, 53, 6509-
6522.
(16) Lemieux, R. U.; Driguez, H. J. Am. Chem. Soc. 1975, 97, 4069-
4083.
(17) Garegg, P. J.; Norberg, T. Carbohydr. Res. 1976, 52, 235-240.
(18) Qin, H.; Grindley, T. B. J. Carbohydr. Chem. 1994, 13, 475-490.
(19) Ford, M. J.; Ley, S. V. SynLett 1990, 255.

Synthesis of a NeuroactiVe Glyconucleoside Disulfate
J. Am. Chem. Soc., Vol. 121, No. 24, 1999 5663
Scheme 3a
Scheme 5a
a Conditions: (a) TBSCl, imidazole, DMF, 2 h; (b) 9, ZnBr2, CH2Cl2,
reflux, 1 h; (c) Bu4NF, THF, 20 h.
bis-silyl ether 12 with the activated fucosyl donor 9 to afford
R-linked glycoside 14 as the exclusive product. Fluoride-induced
desilylation of 14 furnished diol 15, which was smoothly
sulfated using excess SO3‚DMF complex to give disulfate 16.
Purification at this stage either by HPLC or by ion-exchange
chromatography was difficult because of the amphiphilic
characteristics of 16. Deprotection of 16 by exhaustive hydro-
genolysis on Pd(OH)2, followed by HPLC purification (reversed-
phase, H2O/CH3CN/TFA), furnished the desired compound 3.
a Conditions: (a) Cbz-imidazole, KH, 18-crown-6, THF, 2 h; (b)
1:1 TFA/CH2Cl2, 2 h; (c) Bu4NF, THF, 20 h.
Scheme 4a
1
From the H NMR spectrum of 3, it was evident that H2′ and
H3′ on the ribose ring were deshielded by 1.14 and 1.12 ppm,
respectively, compared to the corresponding resonances in 15,
as would be expected from sulfation at the 2′- and 3′-hydroxyl
groups. Moreover, the negative ion FAB mass spectrum revealed
fragments at m/z 652 (M - 2H + Na) and 630 (M - H) in
support of its assigned structure. However, comparison of the
NMR spectrum of synthetic 3 with that of HF-7 revealed that
the two compounds were not identical.
Turning next to glycosylated nucleosides 1 and 2 as candi-
dates for the structure of HF-7, the direct coupling of 8 with
guanosine 2′,3′-diol 17 (Scheme 5) was investigated as an
expedient approach to both 1 and 2. Ether 17, prepared by
monosilylation of 13, underwent a smooth, ZnBr2-catalyzed
reaction with 8 in CH2Cl2 at reflux to afford both the 2′- and
3′-coupled products 18 and 19 in 38% and 40% yields,
respectively. In addition, the corresponding 2′,3′-difucosylated
nucleoside (structure not shown) was obtained in 8-10% yield.
Both 18 and 19 were readily obtained pure by flash column
chromatography, and each could be desilylated in excellent yield
to afford 20 and 21, respectively. Structural assignments were
confirmed at this stage by HMBC NMR spectroscopy, which
indicated long-range coupling of the fucose anomeric hydrogen
H1′′ with the C2′ carbon of 20 and with the C3′ carbon of 21.
The corresponding couplings of the fucose C1′′ with H2′ of 20
and H3′ of 21 were also observed.
a Conditions: (a) 9, CH2Cl2, ZnBr2; (b) Bu4NF, THF; (c) SO3‚DMF;
(d) H2, Pd(OH)2, 23% from 15.
The N-carbobenzoxy group (Cbz) was chosen to protect the
guanine’s primary amine group during the glycosylation step,
since both the Cbz and fucose benzyl ethers could subsequently
be removed by hydrogenolysis under conditions that would not
deacetylate the fucose ring. Only one report appeared on the
use of Cbz group to protect the exocyclic amino group of
nucleoside bases. The paper described a lengthy route to the
N-Cbz derivative of 2-deoxyguanosine, but not of guanosine
itself.20 Therefore, the approach indicated in Scheme 3 was
developed. Reaction of the known21 tris-silyl ether 10 with Cbz-
imidazole22 afforded the Cbz-protected nucleoside 11 in excel-
lent yield. Selective deprotection of 11 to alcohol 12 was
achieved using 1:1 TFA/CH2Cl2, whereas exhaustive desilylation
with fluoride afforded NCbz-guanosine (13).
With appropriate fucose and guanosine building blocks in
hand, a regioselective synthesis of 5′-O-(4′′-O-acetyl-R-L-
fucopyranosyl)guanosine-2′,3′-disulfate (3) was developed, as
shown in Scheme 4. Fucosylation of guanosine selectively at
the 5′-position was achieved by ZnBr2-catalyzed coupling of
The 2′-fucosylated nucleoside 20 underwent sulfation using
excess SO3‚DMF to afford disulfate 22, which, without
purification, was hydrogenolyzed over Pd(OH)2 to afford 2′-
O-(4-O-acetyl-R-L-fucopyranosyl)-guanosine-3′,5′-disulfate (1)
in 36% yield (Scheme 6). Examination of the NMR spectrum
of 1, taken after HPLC purification, revealed significant
differences from that of authentic HF-7 under the same
conditions.
(20) (a) Watkins, B. E.; Rapoport, H. J. Org. Chem. 1982, 47, 4471-
4477. (b) Watkins, B. E.; Kiely, J. S.; Rapoport, H. J. Am. Chem. Soc.
1982, 104, 5702-5708.
(21) Ogilvie, K. K.; Schifman, A. L.; Penney, C. L. Can. J. Chem. 1979,
57, 2230-2238.
By analogy with 20, the major coupling product, 3′-
fucosylated nucleoside 21, was sulfated, and the resulting
(22) Babad, E.; Ben-Ishai, D. J. Heterocycl. Chem. 1969, 6, 235-238.

5664 J. Am. Chem. Soc., Vol. 121, No. 24, 1999
McCormick et al.
Scheme 6a
Scheme 7a
a Conditions: (a) SO3‚DMF, 0 °C to room temperature, 21 h; (b)
H2, Pd(OH)2, 1:1 EtOH/H2O, room temperature, 84 h, 36% from 20;
(c) SO3‚DMF, room temperature, 2 h, 99%; (d) H2, Pd(OH)2, 12:12:1
CH3OH/H2O/TFA, room temperature, 16 h, 95%.
a Conditions: (a) BOC-anhydride, DMAP, Et3N, DMSO, room
temperature, 4 h; (b) TBSCl, imidazole, DMF, room temperature, 12
h; (c) Cbz-imidazole, KH, 18-crown-6, THF, room temperature, 2 h;
(d) TMSOTf-collidine, CH2Cl2, room temperature, 1 h.
disulfate 23 was deprotected by hydrogenolysis to afford 3′-
O-(4′′-O-acetyl-R-L-fucopyranosyl)guanosine-2′,5′-disulfate (2)
(Scheme 6). The high-resolution MS and UV spectra, as well
as 1H and 13C NMR spectra (D2O-TFA, pH 1.8), of synthetic
2 matched those of natural HF-7. Moreover, the 1H NMR
spectrum of a 1:1 mixture of synthetic 2 and HF-7 was
indistinguishable from spectra of each pure component. Taken
as a whole, the spectroscopic data indicated that the structure
of HF-7 was either 2 or its mirror image.
Scheme 8a
Synthetic 2 derived from L-fucose and D-guanosine was
levorotatory. However, the limited quantity of HF-7 available
made it impossible to obtain a reliable specific rotation of the
natural product for direct comparison with that of (-)-2.
Unfortunately, neither the natural product nor synthetic (-)-2
displayed any Cotton effect (200-350 nm) in its circular
dichroism spectrum.
An exhaustive literature search uncovered no naturally
occurring nucleoside or nucleotide that incorporated L-ribose.
To ascertain whether the hexose in naturally occurring HF-7
possessed the D-configuration, the synthesis of 3′-O-(4′′-O-
acetyl-R-D-fucopyranosyl)guanosine-2′,5′-disulfate (4) was car-
ried out using the enantiomer of 9 (Scheme 2) prepared from
D-fucose. As expected, the 1H NMR spectra of synthetic 4 and
natural HF-7 showed distinct, though minor, differences, leading
to the conclusion that HF-7 has the structure and absolute
configuration depicted in 2.
With HF-7 fully characterized, it became possible to consider
an improved, targeted synthesis of (-)-2. First we explored the
possibility of using 2-N-benzyloxycarbonyl-2′,5′-di-O-tert-bu-
tyldimethylsilyl-guanosine (27) as acceptor molecule in the
fucosylation reaction. Direct disilylation of NCbz-guanosine (13)
with a slight excess of TBSCl afforded mixtures of the 2′,5′-
and 3′,5′-bis-silyl ethers in approximately a 1:1 ratio. Alterna-
tively, guanosine was found to react with BOC anhydride
selectively to afford the 3′-protected nucleoside 24 (Scheme 7).
Silylation of the remaining free hydroxyl group using TBSCl
gave nucleoside 25, which upon reaction with Cbz-imidazole
was transformed into the fully protected guanosine derivative
26. The BOC group was removed selectively using TMSOTf-
collidine23 to afford 27, the desired precursor to 3′-glycosylated
a Conditions: (a) (i) HCl, CH2Cl2, 0 °C, 2 h; (ii) (CH3)3NCH(OEt)2,
CH2Cl2, 18 h, 93%; (b) (i) NaOCH3, CH3OH, 2 h; (ii) TBSCl, CH2Cl2,
pyridine, Et3N, 4 h, 84%; (c) IDCP, 4:1 DCE/Et2O, 3 h; (d) HOAc, 15
h, 75% from 31.
nucleoside 2. However, attempts to bring about the reaction of
27 with fucosyl donor 9 using a variety of catalysts afforded
none of the desired coupling product 28.
The inability to fucosylate guanosyl acceptor 27 was an
incentive to develop an entirely different strategy to synthesize
2 via a sequential stepwise introduction of the O- and N-
glycosidic linkages, followed, after protecting group manipula-
tions, by sulfation and deprotection. Formation of the O-gly-
cosidic linkage commenced as depicted in Scheme 8, with the
(23) Zhang, A. J.; Russell, D. H.; Zhu, J.; Burgess, K. Tetrahedron Lett.
1998, 39, 7439-7740.

Synthesis of a NeuroactiVe Glyconucleoside Disulfate
J. Am. Chem. Soc., Vol. 121, No. 24, 1999 5665
Scheme 9a
36, prepared in situ by treatment of known27 2-N-acetyl-6-O-
(diphenylcarbamoyl)guanine (35) with bis(trimethylsilyl)aceta-
mide, proceeded as expected to afford glycoside 37. Prior to
the installation of the requisite 2′,5′-di-O-sulfate groups, 37 was
subjected to the following sequence of protecting group
manipulations. Desilylation of 37 with fluoride followed by
complete deacylation and subsequent selective O-acetylation
afforded crystalline 38, having a free exocyclic amino function.
Selective deacetylation25 of 38 under mild basic conditions led
to the isolation of diol 39, which was subjected to sulfation
using pyridine-sulfur trioxide complex. Workup and analysis
of the reaction mixture by 1H NMR spectroscopy revealed the
presence of the required di-O-sulfated product 41 and a major
amount (90%) of the corresponding trisulfate 40. Unfortunately,
attempts to suppress the unwanted sulfation of the exocyclic
amino function in 39 were abortive. However, selective N-
desulfation28 could be accomplished under acidic conditions (i.e.,
0.2 N H2SO4, 18 h) without affecting the integrity of the
glycosidic linkages, as gauged by 1H NMR spectroscopy.
Accordingly, exposure of a mixture containing 40 and 41 (9:1
ratio) to the same acidic conditions gave, after ion-exchange
(Dowex Na+ form) and purification (Sephadex LH-20), the
homogeneous di-O-sulfated product 41 in an excellent yield.
Hydrogenolysis of 41 over Pd(OH)2 on carbon led, without
further purification, to the isolation of HF-7 (Na+ salt) in near-
quantitative yield. Synthetic HF-7 was levorotatory and indis-
tinguishable from the natural material by reversed-phase HPLC,
NMR spectroscopy, and mass spectrometry.
a Conditions: (a) 35, BSA, DCE, 80 °C, 15 min; (b) 34, TMSOTf,
toluene, 80 °C, 3 h (two steps, 80%); (c) (i) 3HF‚Et3N, pyridine, 6 h;
(ii) 25% NH4OH, CH3OH, 60 °C, 24 h; (iii) Ac2O, pyridine, 8 h (three
steps, 67%); (d) 0.02 M K2CO3, 2:1 CH3OH/CH2Cl2, 22 h; (e) SO3‚pyr,
pyridine, 55 °C, 4 h; (f) 0.2 N H2SO4, 12 h (95% based on 37); (g) H2,
10% Pd(OH)2/C, 10:5:1 CH3OH/H2O/AcOH, 15 h, 99%.
In conclusion, the results described in this paper characterize
HF-7, a new neuroactive compound, as 3′-O-(4′′-O-acetyl-R-
L-fucopyranosyl)guanosine-2′,5′-disulfate (2) and detail two
independent syntheses of this novel spider venom component.
transformation24 of commercially available ribofuranose 29 into
the rigid 1,2-ortho ester 30. Debenzoylation of 30 and subse-
quent regioselective silylation with TBSCl gave the partially
protected ribosyl acceptor 31. Fucosylation of the exposed 3-OH
group in 31 with a slight excess of the highly potent and strongly
R-directing ethyl 4-O-acetyl-2,3-di-O-benzyl-1-deoxy-1-thio-â-
L-fucopyranoside (32)25 under the influence of the mild promoter
iodonium di-sym-collidine perchlorate (IDCP) yielded, after
flash chromatography, the R-linked coupling product 33,
contaminated with a small amount of 32. Acid-mediated ring-
opening of the 1,2-ortho ester 33 under anhydrous conditions
afforded â-acetate derivative 34, thus setting the stage for the
introduction (Scheme 9) of the â-linked guanyl moiety according
to the well-known26 Vorbru¨ggen procedure. Thus, TMSOTf-
assisted condensation of 34 with persilylated guanine derivative
Acknowledgment. We thank the National Institutes of
Health (NIH) for generous financial assistance (GM 35712 to
B.G.; AI12020 and GM 53830 to J.M.; GM 07273 training grant
fellowship to K.M.). Support of the Cornell NMR Facility by
the National Science Foundation (CHE 7904825; PGM 8018643)
and NIH (RR02002) is gratefully acknowledged.
Supporting Information Available: Experimental proce-
dures as well as spectroscopic and physical characterization data
for all new compounds (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
JA990274Q
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