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Pure Appl. Chem., 2011, Vol. 83, No. 3, pp. 699-707

Published online 2011-01-31

Selective transformations of cephalostatin analogues

Mansour M. Nawasreh

Applied Sciences Department, Faculty of Engineering Technology, Al-Balqa Applied University, P.B. 15008, Marka, 11134 Amman, Jordan

Abstract: The highly tumor inhibitory cephalostatins (e.g., cephalostatin 1), a marine natural product isolated from Cephalodiscus gilcristi, have attracted us to synthesize biologically active analogues. The goal of this study is to shed more light on selective desymmetrization of a symmetrical starting analogue through the F-ring opening route applied to certain analogues using different borane complexes. Previously, we have reported a selective opening of the spiroketal in the northern part of an analogue using catechol-borane and D-(N-tosyl) valine-borane complexes. We demonstrate here the possibility of opening the southern part of the same analogue using salicylic acid-borane complex by which extra flexibility is harvested. In contrast, a different reaction type took place when another analogue was treated with 3,4-diaminobenzonitrile-borane complex, which give after H2O2 oxidation, products arising from ∆14 bond hydration. This led us to conclude that the geometry of both borane complex and substrate govern the regioselectivity of the products. However, the electronic nature of both substrate and borane-complex govern the chemoselectivity.