PREGNANE GLYCOSIDES FROM STAPELIA-VARIEGATA

Eleven new pregnane ester glycosides have been isolated from the aerial parts of Stapelia variegata. Eight of the recognized compounds were established to possess the same trioside moiety, viz. 3-O-[3-O-methyl-6-deoxy-beta-D-allopyranosyl-(1-4)-beta-D-cymaropyranosyl-(1-4)-beta-D-cymaropyranoside]. These compounds were identified as: stavaroside A: 12-O-beta-angeloyl-20-O-benzoyl sarcostin; stavaroside B: 12-O-beta-angeloyl-20-O-tigloyl sarcostin; stavaroside C: 11 alpha-acetoxy 2 beta-benzoxy-3 beta,8 beta,14 beta-trihydroxy-pregn-5-ene-20-one; stavaroside D: 11 alpha-acetoxy-12 beta-tigloxy-3 beta,8 beta,14 beta-trihydroxy-pregn-5-ene-20-one; stavaroside E: 12-O-beta-benzoyl sarcostin; stavaroside F:11 alpha-acetoxy- 12 beta-acetoxy-3 beta, 8 beta, 11 beta, 12 beta, 14 beta-trihydroxy-pregn-5-ene-20-one; stavaroside G: 12-O-beta,20-O-diacetyl sarcostin and stavaroside H: 3 beta, 8 beta, 11 alpha, 12 beta, 14 beta-pentahydroxy-pregn-5-ene-20-one. The other three compounds were shown to possess the same tetraside sugar moiety, Viz. 3-0- [beta-D-glucopyranosyl-(1-4)-3-O-methyl- 6-deoxy-beta-D-allopyranosyl-(1-4)-beta-D-cymaropyranosyl-( 1-4)-beta-D-cymaropyranoside]. These compounds were identified as: stavaroside I: 1 alpha, 12 beta-angeloxy and benzoxy-3 beta, 8 beta, 14 beta-trihydroxy-pregn-5-ene-20-one; stavaroside J: 11 alpha-acetoxy-12 beta-benzoxy-3 beta,8 beta, 14 beta-trihydroxy-pregn-5-ene-20-one and stavaroside K: 11 alpha-acetoxy-12 beta-tigloxy-3 beta,8 beta,14 beta-trihydroxypregn-5-ene-20-one. The structural elucidation of the isolated compounds was aided significantly on the basis of the chemical and spectral evidence. The decisive assignments of the ester positions were based on the Inverse Detected-Heteronuclear Multiple Bond Connectivity (HMBC) experiments.