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 1 1 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 respective groups have independently reported the total synthesis and stereochemical revision of aeruginosin 298-A utilizing L- tyrosine as a starting material. 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 acid 8 capitalized on the prospects of a ring-closure metathesis reaction 9 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 chemistry 12 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 BF 3 .Et 2 O 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 method 9 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 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 pseudodiaxial 14 carbomethoxy group on the concave face of the bicyclic motif, as evidenced by X-ray analysis (Scheme 1). The synthesis of the Δ-3 pyrroline unit 15 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 reaction 9 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. Figure 1. Disconnection of dysinosin A to subunits and chirons. Scheme 1 a a Reagents and conditions: (a) 1. TFA, CH2Cl2; 2. NaHCO3; 3. Δ, 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, ( i Pr)2NEt, CH2Cl2; 98%. (g) Pd/C 20%, H2,MeOH; 95%. Published on Web 10/17/2002 13342 9 J. AM. CHEM. SOC. 2002, 124, 13342-13343 10.1021/ja0208153 CCC: $22.00 © 2002 American Chemical Society