The absolute stereochemistry of the enzymic cyclisation to form the sterpurene sesquiterpenes

✍ Scribed by Chris Abell; Andrew P. Leech

• Publisher: Elsevier Science
• Year: 1988
• Tongue: French
• Weight: 246 KB
• Volume: 29
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)80491-8

✦ Synopsis

Incorporation studies using [I ,2-13Cz]acetate into a novel sterpurene sesquitetpene, 9,12-dihydroxysrerpurene (I), have allowed the absolute stereochemistry of the emymic cyclisation offarnesyl pyrophsphate to sterpurene to be elucidated. Observation of two-bond 13C-13C coupling across the cyclobutane ring confirms the derivation of these two carbon atonzzfrom the same acetate unit. The sterpurenes comprise a recently discovered group of sesquiterpene metabolites from the fungus Stereum purpureum. They are character&d by the tricyclic skeleton of the parent hydrocarbon sterpurene (l).' Biosynthetic experiments have established the isoprenoid nature of these compounds* and shown that the enzymic cyclisation of farnesyl pyrophosphate to sterpurene proceeds with carbon-carbon bond cleavage.3 In this paper we present biosynthetic results on a novel sesquiterpene. 9,12dihydroxysterpurene (2), which provide detailed stereochemical information on the enzymic cyclisation of farnesyl pyrophosphate and further insight into the rearrangement reaction involved in setting up the cyclobutane ring of sterpurene. Cane has proposed that the two antipotlal classes of cyclopentane sesquiterpenes are formed by enantiomeric folding of the famesyl pyrophosphate precursor in the corresponding cyclase enzyme active sites.4 It is proposed that attack of the C-l cation, formed by departure of the allylic pyrophosphate, on either the si or re face of the terminal double bond generates humulene or humulyl cations in enantiomeric conformations, which