Stereoselective synthesis of the enantiomer of the novel marine diterpene isoagatholactone, ent-13(16),14-spongiadien-12.alpha.-ol, and the parent hydrocarbon isocopalane from methyl isocopalate

Mycgranol, a new diterpene from the marine sponge Mycale aff. graveleyi

Mycgranol, a new isocopalane diterpene (methyl 1beta-hydroxy-2-oxoisocopalanoate) was isolated from the Kenyan sponge Mycale (Aegogropila) aff. graveleyi. The structure of the compound was elucidated by interpretation of MS, COSY, HMQC, HMBC, and ROESY data. The absolute configuration of mycgranol was determined to be the same as that of the nudibranch isocopalane diterpenes rather than that of the ent-compounds known from sponges of the genus Spongia.

Synthesis of C-17-functionalized spongiane diterpenes: diastereoselective synthesis of (-)-spongian-16-oxo-17-al, (-)-acetyldendrillol-1, and (-)-aplyroseol-14

The diastereoselective synthesis of spongiane diterpenes (-)-spongian-16-oxo-17-al 2, (-)-acetyldendrillol-1 15, and (-)-aplyroseol-14 16 has been completed efficiently via the common intermediate 14. Compound 14 was prepared in five synthetic steps from (+)-podocarp-8(14)-en-13-one 13, easily available from commercial (-)-abietic acid. The key steps in the syntheses were a regioselective reduction of a 1,4-dialdehyde unit, a one-pot acetalization-acetylation, and a translactonization. The synthesis of 15 and 16 has led us to a revision of the configuration at C-17 for natural (-)-acetyldendrillol-1 and a structural reassignment for aplyroseol-14. Thus, aplyroseol-14 16 presents an unprecedented delta-lactone-based structure for spongiane-type diterpenoids. A theoretical study including a series of ab initio calculations for the mechanism involved in the conversion of ester 22 into natural product 2 has also been carried out.