The carbon-13 nuclear magnetic resonance spectrum of junipal

✍ Scribed by Milton T.W. Hearn

• Publisher: Elsevier Science
• Year: 1975
• Tongue: French
• Weight: 197 KB
• Volume: 16
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)75240-3

✦ Synopsis

Junipal (I), a neutral metabolite isolated from Daedalea juniperina Murr., has been known' for twenty years and, until recently, represented the only known fungal polyacetylenic thiophen. Re-investigation of the fungus has however revealed' the presence of two further thiophens (II, R = CH(OH)CH3) and, (II, R = COCH3). The rationale for the structure of these novel metabolites has come from spectroscopic methods and chemical synthesis*. CH @+ CHO 3 (I) COR CH3 (II) Biosynthetic studies using 14C-labelled substrates have shown3 that junipal, in consnon with other CB-polyacetylenes, may arise via the crepenynate pathway with the terminal eight carbons of crepenynate providing the carbon skeleton (Scheme). Bohlmann4 has concluded from biosynthetic studies with higher plants that thio-enol ethers can act as intermediaries in the biogenesis of thiophen metabolites. This is an attractive hypothesis for the origin of junipal, although the detailed biomechanisms involved in the ring cyclisation and oxidative loss of the two proximal carbon atoms from a dehydromatricaria ester precurser remain to be clarified. In the tribus Anthemideae, which is well known4 for its ability to elaborate a range of polyacetylenic thiophen metabolites derived from dehydromatricaria ester, the common presence of f3-2-(5-propynyl)-thienylacrylic acid would suggest that cyclisation in higher plants, and possibly also in fungi, occurs at the CIo stage prior to the function group modifications. Scheme Oleate c Crepenynate + *CH3.