Manzamenones

Manzamenone J (66) had the same composition as manzamenone D (61) with a conjugated dienone (Xmax 317 nm) functionality. Analysis of several types of 2D NMR spectra of 66 led to a bicyclo[4.3.0]nonane ring system involving a l(6),2-dien-7-one chromophore. The stereochemistry of the vicinal methine protons on C-8 and C-9 were suggested to be anti from the NOESY spectrum of 66 showing substantial correlations from H-8 to H2-26 and H2-27. The stereochemistry of C-5 position relative to C-8 and C-9 portion remained unassigned. 

In connection with the biogenetic path of manzamenones and related Plakortis metabolites, we isolated 3-carboxy-5-(carboxymethyl)-4-tetradecyl-l-oxacyclopent-3-en-2-one (73) [38] from the same Plakortis sponge collected off Manzamo. The structure of compound 73 was defined by extensive spectroscopic analyses. On treatment with diazomethane compound 73 was converted into a dimethyl ester (74), indicating the presence of two carboxylic acids. From the 2D NMR studies, compound 73 was suggested to have a y-butenolide structure with... 

Scheme 5. Another hypothesis on the biogenesis of Manzamenone A (52) and Untenone A (77).

Ishibashi, M., Takeuchi, S., and Kobayashi, J. (1993b) Untenone A, a new cyclopentenone from the Okinawan marine sponge Plakortis sp. corresponding to the dienophile in the biosynthesis of manzamenones. Tetrahedron Lett., 34, 3749-3750. 

Doncaster, J.R., Etchells, L.L., Kershaw, N.M., Nakamura, R Ryan, H., Takeuchi, R Sakaguchi, K Sardarian, A., and Whitehead, R.C. (2006) Synthetic analogues of the manzamenones and plakoridines which inhibit DNA polymerase. Bioorg. Med. Chem Lett., 16, 2877-2881. 

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