Synthesis and biological assessment of hemiacetal spiro derivatives towards development of efficient chemotherapeutic agent

We have developed an efficient construction of spiro derivatives by anodic oxidation of the corresponding phenols, which enabled synthesis of spiroisoxazoline natural products as well as heliannuols, carrying chroman and benzooxepin structures. In addition to nucleophilic attack of hydroxyl or amino groups to the cation generated electrochemerically, it might be of interest to use a carbonyl oxygen as a nucleophilic center, which would provide hemiacetal-type spiro compounds. Gymnastatin A 1 was isolated from the strain of Gymnescella dankaliensis separated from the sponge Halichondria japonica, together with other gymnastatins. This marine natural product consists of the spiro structure between the dienone part including two chlorine atoms, and the tetrahydrofuran ring with a hemiacetal moiety, along with the fatty acid part having an asymmetric carbon center attached with the amino group. As part of our extensive electrochemical investigation of halogenated tyrosine derivatives, synthesis of the acetal-spiro derivatives and its application to gymnastatin A 1 was undertaken to develop further efficient and green sustainable methodology. In these investigations, construction of spiro compounds having hemiacetal moiety, and synthesis of gymnastatin A 1 was achieved successfully. In addition to the synthesis, biological assessment of synthetic samples was examined. Among them, 3, 5, 14, and 15 showed a wide range of inhibitory activity against Gram-positive, -negative bacteria, fungus, and Mycobacterium.