Total synthesis and structural confirmation of the marine natural product dysinosin A: A novel inhibitor of thrombin and Factor VIIa

Article abstract of DOI:10.1021/ja0208153

The structure and absolute configuration of the marine antithrombotic product dysinosin A was confirmed by total synthesis. The strategy involved disconnections to three subunits, of which two were synthesized from the readily available l-glutamic acid, d

Full text of DOI:10.1021/ja0208153

Published on Web 10/17/2002
Total Synthesis and Structural Confirmation of the Marine Natural Product
Dysinosin A: A Novel Inhibitor of Thrombin and Factor VIIa
Stephen Hanessian,* Roberto Margarita, Adrian Hall, Shawn Johnstone, Martin Tremblay, and
Luca Parlanti
Department of Chemistry, UniVersite´ de Montre´al, C.P. 6128, Succursale Centre-Ville,
Montre´al, Que´bec H3C 3J7 Canada
Received June 7, 2002
The marine natural product dysinosin A 11 is a new member of
serine protease inhibitors generally known as the aeruginosins
(Figure 1).2 It exhibits activity against thrombin, an essential enzyme
in the blood coagulation cascade,3 and Factor VIIa which is involved
in blood vessel damage in complex with tissue factor (TF).4 The
structure of dysinosin A was determined by detailed NMR studies
and its absolute stereochemistry deduced from an X-ray structure
of a complex with thrombin.1 Dysinosin A possesses unique
structural and functional features that distinguish it among the
aeruginosins. Noteworthy is the presence of a 5S,6R-dihydroxy
octahydroindole carboxylic acid, an unusual guanidine as part of a
pyrroline ring,2d,5 and a sulfate group. Bonjoch,6 Wipf,7 and their
Figure 1. Disconnection of dysinosin A to subunits and chirons.
respective groups have independently reported the total synthesis
and stereochemical revision of aeruginosin 298-A utilizing L-
tyrosine as a starting material.
Scheme 1 a
We report herein the total synthesis of dysinosin A utilizing a
carbon construct strategy that generates subunits originating from
L-glutamic acid, butyrolactone, D-leucine, and D-mannitol as shown
in Figure 1. The synthesis of the enantiopure octahydroindole
carboxylic acid8 capitalized on the prospects of a ring-closure
metathesis reaction9 from a chiron derived from L-pyroglutamic
acid, and subsequent stereoselective epoxidation and epoxide
opening. To this end we had to secure methodology that introduced
two C-allylic appendages with a syn-disposition at C-4 and C-5 of
L-proline as shown in Scheme 1. The (4S)-allyl analogues 2 and 3
have been previously synthesized by stereoselective enolate alkyl-
ation of the corresponding L-glutamate esters.10 Conversion of 2
and 3 into the corresponding methyl L-pyroglutamates,11 selective
reduction, and acetylation afforded the expected hemiaminal
derivatives 4 and 5. The introduction of a syn-allyl group at C-5
via N-acyl iminium ion chemistry12 proved to be challenging. After
extensive variations of solvents, the nature of Lewis acids, and
N-substitutents,13 allylation of 5 could be realized with a 5.5:1 all-
syn/anti selectivity with allyl tributylstannane in the presence of
BF3.Et2O in toluene to afford 7, easily separable from the minor
diastereomer by chromatography. Allylation of 4 under the same
conditions led to a 1:2 ratio of syn/anti isomers of 6.
Olefin metathesis of 6 and 7 using the original and elegant
Grubbs method9 led to the carbocyclization products 8 and 9,
respectively, in excellent yields. Epoxidation with m-CPBA proved
to be highly selective, affording the epoxides 10 and 11 in each
case, presumably as a result of an attack from the more accessible
convex face of the bicyclic system. When treated with aqueous
TFA, each epoxide led to the enantiopure intermediates 12 and 13,
respectively, whose structures were unequivocally proven by single-
crystal X-ray analysis. For reasons of functional group compatibility,
the synthesis was continued with 13, which was transformed to
a Reagents and conditions: (a) 1. TFA, CH2Cl2; 2. NaHCO3; 3. ∆,
toluene; 4. LiHMDS, CbzCl, THF -78 °C; 5. LiHBEt3, THF -78 °C; 6.
Ac2O, DMAP, CH2Cl2; overall 85%. (b) BF3.OEt2, allyl tributylstannane,
toluene -78 °C (syn/anti 5.5:1); overall 83%. (c) Ru benzylidene(Cy3P)2Cl2
1 mol %, CH2Cl2; 99%. (d) m-CPBA, CH2Cl2. (e) TFA (0.2 equiv),THF/
H2O (1/1); 75-79% (2 steps). (f) MOMCl, (iPr)2NEt, CH2Cl2; 98%. (g)
Pd/C 20%, H2,MeOH; 95%.
the bis-MOM ether 14. The highly site-selective trans-diaxial acid-
catalyzed opening could be due in part to the shielding effect of
the pseudodiaxial14 carbomethoxy group on the concave face of
the bicyclic motif, as evidenced by X-ray analysis (Scheme 1).
The synthesis of the ∆-3 pyrroline unit15 shown in Scheme 2,
started with the hydroxy ester 15 readily available from butyro-
lactone.16 Reduction of the ester function gave the allylic alcohol
16,17 which was further transformed to the diolefin 17 in high
overall yield. The versatility of the Grubbs metathesis reaction9
and its tolerance of functional groups was evidenced by the
* To whom correspondence should be addressed. Telephone: (514) 343-6738.
Fax: (514) 343-5728. E-mail: stephen.hanessian@umontreal.ca.
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J. AM. CHEM. SOC. 2002, 124, 13342-13343
10.1021/ja0208153 CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Scheme 2 a
Acknowledgment. Dedicated to Professor Robert H. Grubbs
for his seminal work in olefin metathesis. We thank NSERCC for
generous financial support from AstraZeneca (Mo¨lndal Sweden)
through the Medicinal Chemistry Chair Program. We appreciate
the enthusiastic support given by Dr. David Rees and Dr. Kenneth
Granberg (AstraZeneca). We also thank Elaine Fournelle for HPLC
analyses and Dr. Michel Simard for X-ray analyses. M.T. acknowl-
edges scholarships from NSERC and FCAR.
Supporting Information Available: Experimental procedures of
key reactions, NMR, and X-ray and other data (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
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The acyclic peptide chain 22 was prepared as shown in Scheme
3 from D-leucine and 2-O-methyl-D-glyceraldehyde easily available
from D-mannitol.19 Peptide coupling between 14 and 22 afforded
23 which was hydrolyzed to the free acid. A second peptide
coupling with 20 proceeded in good overall yield to give 24, which
was desilylated to the alcohol 25. Treatment of 25 with pyridine-
SO3 complex in dichloromethane in the presence of a catalytic
quantity of dibutyltin oxide20 afforded the corresponding sulfate
ester. Hydrolysis of the N-Boc group with TFA in dichloromethane,
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reverse phase HPLC afforded dysinosin A as a white solid, identical
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1
in all respects to the natural product (HPLC, H,13C NMR, FAB
(19) Nicolaou, K. C.; Piscopio, A. D.; Bertinato, P.; Chakraborty, T. K.;
and electrospray mass spectrometry).
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53, 16391. (c) Martinelli, M.; Vaidyanathan, R.; Pawlak, J. M.; Nayyar,
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V. V.; Kosmrlj, B. J. Am. Chem. Soc. 2002, 124, 3578.
The total synthesis of dysinosin A by an enantioselective route
provides definitive evidence for its structural and configurational
identity. It also represents the first total synthesis of a hitherto
unknown member of the aeruginosin family of marine antithrombin
natural products, with inhibitory activity against Factor VIIa.
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