Cuparane

Acherar, S. Audran, G. Vanthuyne, N. Monti, H. Use of lipase-catalyzed kinetic resolution for the enantioselective approach toward sesquiterpenes containing quaternary centers the cuparane family. Tetrahedron Asymmetry 2003, 14,2413-2418. 

A series of new examples has recently emerged in the literature. Aquaticol (10), an unusual cuparane-type bis-sesquiterpene isolated from the medicinal plant Veronica anagailis-aquatica, can be derived from a Diels-Alder cyclodimerization of the ortfco-quinol 11, itself derived from an enantiospecific oxidative hydroxylation of (—)-d-cuparenol (12) (Figure 5) [37, 38]. Sorbicillinoid members of the vertinoid polyketide class of natural products also present the same chemical filiation inasmuch as they appear to originate biosynthetically from the sorbicillinol (13)-derived ortho-quinol 14 (Figure 6) (Section 15.3.3) [39, 40]. 

The transition from the bisabolane skeleton to the cuparane is not favourable energetically. Initially a secondary carbocation is formed from a tertiary, though a hydrogen shift quickly moves the positive charge back to a tertiary centre. The five-membered ring which is formed is very cluttered and, therefore, suffers from steric strain. The driving force must, therefore, come from the protein which catalyses the reaction. The 1,2-carbon shift to the chamigrane skeleton relieves some of the steric strain but this creates a spiro centre, the strain of which is relieved by the 1,2-carbon shift which creates the thujopsane skeleton. 

Cuparane, Thujopsane, Chamigrane, Acorane, Alaskane, Cedrane, Zizaane, and Trichothecane... 

A short synthesis of the ketone (95) has been reported and this constitutes a formal synthesis of cuparene (96), since (95) has been converted into (96) previously. As an alternative strategy to the cuparane skeleton a three-carbdn... 

Sesquiterpene quinones of the cuparane type from cultures of the inky caps Coprinus lagopus, C. cinereus, and C. macrorhizus (Basidiomycetes). The wild forms of these mushrooms do not form lagopodins. L A CijHigOj, Mr 246.31, yellow cryst., (ali, -10 (CHClj), L. B (C,5H,g04, Mr 262.31), and hydroxy-L B (CijHigOj, Mr 278.30, orange red cryst., mp. 184-186 C) have been described. Both L. A and L. B are unstable in aqueous solution and ex-... 

Hashimoto, T., Y. Noma, andY. Asakawa, 2006. Biotransformation of cuparane- and herbertane-type sesquiterpenoids. Proceedings of 50th TEAC, pp. 263-265. 

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). 

These results establish that both antipodes, (-h)- and (—)-, of cuparane-type sesquiterpenoids occur in the Hepaticae. 

Matsuo, A., I. Terada, M. Nakayama, and S. Hayashi Cuprenenol and Rosulantol, a New Cuparane Class Sesquiterpene Alcohols from the Liverwort Jungermannia rosulans. Tetrahedron Letters 1977, 3821. 

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