Furanocoumarin and Furanoquinoline Derivatives

Furanocoumarin and Furanoquinoline Derivatives.—The two extra carbon atoms of these furanoid rings are derived from C 4,5 of mevalonic acid. Probably very similar processes occur in both types of secondary metabolites. For ex-ample, psoralen (21 R = H) and bergapten (21 R = OH) are derived from umbelliferone (18) via marmesin (19) and their dihydro-derivatives (20). An 

Rapid advances have been made in the study of the relatively rare cyclopentanoid monoterpenoids due to their involvement in indole alkaloid biosynthesis. The bismonoterpenoid foliamenthin (26) was discovered in these studies and Arigoni and co-workers have demonstrated the efficient incorporation of geraniol (27) into both halves of (26). Battersby obtained similar results with 6,7-dihydro-foliamenthin. In both cases, as expected, the acyclic half is more radioactive. 

The acyclic precursor of the monoterpenoids is normally assumed to be geranyl pyrophosphate (6 n = 1) but, clearly, this cannot directly cyclise to the foliamenthin skeleton. Two alternative precursors are linalool pyrophosphate (28 R = P206 ) and nerol pyrophosphate (29 R = P206 ). Unfortunately, 

Szczepanski, J. Coscia, and D. Arigoni, Chem. Comm., 1968, 1276. 

1-H of loganin (35 R = Me). However, the first Cjo acyclic precursor must be geranyl pyrophosphate 6 n = 1) since two tritium atoms are incorporated by the [2- C,3R,4R- H]isomer and none by the (4S)-isomer. The mechanism proposed by Arigoni for this cyclisation involves the trialdehyde (33). Potty et al. have isolated an enzyme from Citrus spp. which oxidises geraniol (27) to the corresponding aldehyde. 

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