Cinatrin C1

The stereocontrolled total synthesis of (-)-cinatrin C1, a phospholipase A2 inhibitor, has been accomplished. The key feature includes the stereoselective construction of the highly substituted tetrahydrofuran core by In(OTf)3-catalyzed Conia-ene reaction of the oxygen-tethered acetylenic malonic ester followed by dihydroxylation with concomitant lactonization.

Cinatrins A, B and C3 inhibited phospholipase A2 purified from rat platelets in a dose-dependent manner. Cinatrin C3, the most potent component (IC50 70 microM), was noncompetitive with a Ki value of 36 microM. Cinatrins B and C3 also inhibited both porcine pancreas and Naja naja venom phospholipase A2. Inhibition of rat platelet phospholipase A2 by cinatrin C3 was independent of Ca2+ and substrate concentration. Comparison with duramycin, another phospholipase A2 inhibitor, displayed inhibition dependent on substrate concentration when phosphatidylethanolamine was the substrate. These results indicate that the inhibition of phospholipase A2 by cinatrin C3 may result from direct interaction with the enzyme.

The enantiospecific synthesis of (-)cinatrin C1 (3) and (+)-cinatrin C3 (5) from the D-arabinose derivative 9 is described. The stereochemistry at C2 was introduced via a chelation-controlled addition of a carbanion to alpha-hydroxy ketone 8. The best selectivity was achieved by use of the Grignard reagent derived from trimethylsilylacetylene. Transformation of the terminal alkyne into methyl ester 17 followed by acetal hydrolysis and selective lactol oxidation gave cinatrin C1 dimethyl ester (7). Base hydrolysis and acid induced relactonization then gave a 1:1 mixture of cinatrins C1 (3) and C3 (5).