Madeiranes, a New Class of Pentacyclic Triterpenes: D-Friedo-madeir-14-en-3β-ol and -3-one, D:C-Friedomadeir-7-en-3β-ol and -3-one

The pentacyclic triterpenes 1a, b and 2a, b are isolated from extracts of Euphorbia mellifera Arr. Their structures, determined by X‐ray analysis, are supported in part by MS, NMR, and IR data. The skeleton differs from that of representatives of the lupane or hopane class by (i) an unusual arrangement of the substituents in the cyclopentane ring E, the Me group being on C(19) and the i‐Pr group in an angular position on C(17), and (ii) a cis D/E ring junction. We propose to name Die unknown pentacyclic parent ‘madeirane’, thus 1a, b and 2a, b are D‐friedomadeir‐14‐ene and D:C‐friedomadeir‐7‐ene derivatives. The biosynthesis of these compounds may be rationalized via ‘spirodammaranol’‐cation intermediates 5 and 5′ and madeiranol cation 6, as outlined in Scheme 2.