Browsing by Author "SUAREZ, E"
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- ItemACID-CATALYZED REARRANGEMENT OF TREVOAGENIN-A AND TREVOAGENIN-B - THE ACETAL FUNCTION AS ELECTRON-DONOR GROUP IN HETEROLYTIC FRAGMENTATIONS(1983) FRANCISCO, CG; FREIRE, R; HERNANDEZ, R; SALAZAR, JA; SUAREZ, E; CORTES, MThe acid-catalyzed rearrangement of trevoagenins A (1) and B (4) [constituents of Trevoa trinervis] gave 3.beta.-hydroxy-24-oxo-16,17-sec-5.alpha.-dammar-17(20)E-ene-16,30-lactone (5) (40%), its 17(20)Z-ene isomer (7) (13%), and (20R,24R)-3.beta.,25-dihydroxy-15.alpha.,30-cyclo-20,24-epoxy-5.alpha.-dammaran-16-one (9) (2%). Compounds (5) and (7) were produced through a heterolytic fragmentation mechanism. In order to study the scope of this rearrangement the C-20 epimeric hydroxy acetals (24) and (28) were synthesized starting from trevoagenin B and A, respectively. The reaction of the 20S-hydroxy acetal (24) with I led to the Z-olefin (29) while the 20R-hydroxy acetal (28) gave the E-olefin (30). The concerted nature of this heterolytic fragmentation, where acetals or hemiacetals are the electron-donor groups, is supported by the observed stereospecificity of the reaction.
- ItemC-13 NMR-STUDY OF (20,24)-EPOXYDAMMARANE TRITERPENES(1984) FRANCISCO, CG; FREIRE, R; HERNANDEZ, R; SALAZAR, JA; SUAREZ, E; CORTES, M
- ItemDAMMARANE TRITERPENES OF TREVOA-TRINERVIS - STRUCTURE AND ABSOLUTE STEREOCHEMISTRY OF TREVOAGENIN-A, TREVOAGENIN-B, AND TREVOAGENIN-C(1983) BETANCOR, C; FREIRE, R; HERNANDEZ, R; SUAREZ, E; CORTES, M; PRANGE, T; PASCARD, CTrevoagenins A, B and C, extracted from T. trinervis Miers, were shown by chemical and spectral means to be isomeric dammarane triterpenes possessing the general 3.beta.,25,30-trihydroxy-(20,24)-epoxydammaran-16-one structure with stereoisomeric side-chains of the ocotillol type.