Three new eicosanoids (l-3) possessing a unique g-membered ring lactone and novel sites of oxidation have been isolated from the colonial marine ascidian Dtimnum caruiiakn (F. Didemnidae). These compounds further illustrate some intriguing differences in the pathways of eicosanoid production between mammals and several marine invertebrates.
In mammalian tissues, the enzymatic oxidation products of eicosapolyenoic fatty acids (EFAs), especially arachidonic acid, are powerful mediators of diverse physiological events such as tumor growth, inflammation, hypersensitivity reactions, bloodclotting and smooth muscle contraction l. Frostaglandins and thromboxanes arise from a cyclooxygenase-derived endoperoxide while various lipoxygenases produce hydroperoxypolyenoic acids @IFETEs) which are converted to leukotrienes and lipoxins. Corey and coworkers2 recently demonstrated that prostanoids present in marine octocorals are produced via a lipoxygenase type pathway rather than the traditional cyclooxygenase oxidation. This intriguing difference in the pathway of prostanoid production between mammals and some marine invertebrates suggests other unique pathways producing eicosanoids may exist in marine organisms.
In this paper, we wish to report on the chemical investigation of the colonial marine ascidian, Didemnum candidum, which contains several new natural products (l-3) that appear to have arisen through a novel 7-lipoxygenation of a Cm fatty acid. These compounds, isolated as 9-membered ring &tones, further illustrate the uniqueness of eicosanoid production in marine invertebrates.