New phenolic triterpenes from Maytenus blepharodes. Semisynthesis of 6-deoxoblepharodol from pristimerin

Four new phenolic triterpenes with a 24-nor-D:A-friedoleane skeleton, isoblepharodol, 7-oxoblepharodol, blepharotriol and 6-deoxoblepharodol, were isolated from Maytenus blepharodes. Their structures were elucidated on the basis of spectroscopic analysis, including homo and heteronuclear correlation NMR experiments (COSY, ROESY, HSQC, and HMBC). The semisynthesis of 6-deoxoblepharodol and its epimer at C-8 was achieved by catalytic reduction of pristimerin, a quinone-methide triterpene present in the plant. The biosynthetic formation of the phenolic triterpenes isolated from this species is also discussed. The compounds were assayed for antimicrobial and cytotoxic activities.