Ophiocerins A−D and Ophioceric Acid:  Tetrahydropyran Derivatives and an Africane Sesquiterpenoid from the Freshwater Aquatic Fungus Ophioceras venezuelense

Abstract

Four new tetrahydropyran derivatives called ophiocerins A-D (1-4) and a new africane sesquiterpenoid (ophioceric acid; 5) have been isolated from cultures of the aquatic fungus Ophioceras venezuelense, together with the known compound regiolone. The structures and relative stereochemistry of these compounds were determined by analysis of 1D and 2D NMR data, while absolute stereochemical assignments for 1-4 were proposed by application of the exciton chirality CD method.

Stereoselective synthesis of ophiocerin B

“…1 The substituted tetrahydropyran moiety is a part structure of a wide variety of natural products with diversified biological functions. 2,3 Ophiocerins A-D (1-4) are a class of natural products isolated from freshwater aquatic fungi by Reategui et al 4 from Ophioceras venezuelense 5 (Magnaporthaceae). The structural analysis of ophiocerins A-D was arrived at by Gloer et a1.…”

“…6 These new tetrahydropyran derivatives appear to be the first isolated natural products from the above genus. 4 Consequently, compounds 1-4 have attracted considerable synthetic attention…”

Synthesis of Ophiocerins from Non-Carbohydrate Sources

“…1 Since substituted tetrahydropyran rings are found in many biologically important natural products, 2 ophiocerins have attracted the attention of synthetic chemists. The Yadav group recently reported the synthesis of ophiocerin B (2) and C (3), 3 whereby asymmetric hydroxylation was used as a key reaction to install the requisite stereochemical centers.…”

Synthesis of Ophiocerin A and B

“…1 Due to the interesting array of substituents on the tetrahydropyran rings, 2 Yadav and coworkers studied the synthesis of ophicerin B (2) and C (3). They used asymmetric dihydroxylation for introducing the required diol stereochemistry.…”

“…Selective tosylation and subsequent base treatement followed by the debenzylation (H 2 , Pd/C) offered ophiocerin B (2) which showed the identical spectral properties to those reported in the literature. 1 We next turned our attention to the synthesis of ophiocerin A (1). Our synthetic scheme for the preparation of ophiocerin A is shown in Scheme 2.…”