Abstract
Cubitene was isolated from the hexane extract of C. umbratus soldier heads by chromatography over Florisil followed by preparative GLC. High resolution mass spectroscopy indicated the formula of cubitene to be C/sub 20/H/sub 32/. Mass spectra of catalytically hydrogenated cubitene products showed peaks at m/rho 279, consistent with their formulation as substituted cycloalkanes of the composition C/sub 20/H/sub 40/. Cubitene is therefore a monocyclic hydrocarbon with four centers of unsaturation. the /sup 1/H NMR spectral data revealed the presence of two 1,1-disubstituted double bonds, and two additional olefinic protons. Four methyl groups attached to double bonds are also observed. The /sup 13/C NMR spectrum indicated the presence of two tribsubstituted double bonds. Fortunately, cubitene could be obtained in crystalline form (mp 34.5-35/sup 0/C) from cold methanol, allowing a single-crystal x-ray diffraction analysis. It crystallized in the monoclinic crystal class. Lattice parameters were: a = 15.963 (5), b = 6.799 (2), c = 17.038 (5) A; theta = 96.99 (2)/sup 0/. Evidence shows cubitene to be 1,5-dimethyl-8,10-bis(isopropenyl)cyclododeca-1,5-diene, a structure in which one isoprene unit is irregularly joined to three others. It appears to be the first example of a diterpene hydrocarbon based on a twelve-membered carbocyclic ring. Its biosynthesis poses interestingmore » problems. Two possible biosynthetic routes are suggested. An even more basic question remains....whether termite soldiers synthesize cubitene at all, or whether they simply sequester it (or a closely related precursor) from their food.« less
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