Cuparene-type sesquiterpenes

Both 1,4- and 1,5-hydrogen rearrangements have been discovered in the biosynthesis of sesquiterpenes and diterpenes. A 1,4-hydrogen transfer occurs in the formation of the bicarbocyclic nucleus of the trichothecane sesquiterpenes, presumably via the parent hydrocarbon trichodiene 35, 207—209). The biosynthesis of helicobasidine, a closely related cuparene-type sesquiterpene, also has a 1,4-hydrogen rearrangement step 210). 

From Jungermannia rosulans, two new cuparane-type sesquiterpenes, cuprenenol (267) and rosulantol (268) have been isolated together with ( + )-cuparene [ = enantiomer of (269)] and ( + )-2-hydroxycuparene [ = enantiomer of (271)] (245). Structure and configuration were assigned to (267) by chemical correlation with (+ )-cuparene, on the basis of the negative Cotton effect exhibited by the a, P-unsaturated ketone (288) derived from (267), and by applying the benzoate rule to diol (292) obtained from an epoxyalcohol (291) (Scheme 33). 

Rosulantol (268) was treated with POCI3 to give ( + )-2-hydroxy-cuparene [=en -(271)]. Oxidation of (268) with Cr03 gave / -hydroquinone (295) and / -quinone (296) (Scheme 34). The chemical evidence and the CD curve of (268) showed that it was a cuparane-type sesquiterpene. The absolute configuration of the hydroxyl group on C-5 was deduced by applying the benzoate rules to a monobenzoate of (294). 

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