On the origin of cytotoxicity of the natural product varacin. A novel example of a pentathiepin reaction that provides evidence for a triatomic sulfur intermediate
A. Greer, On the origin of cytotoxicity of the natural product varacin. A novel example of a pentathiepin reaction that provides evidence for a triatomic sulfur intermediate, J AM CHEM S, 123(42), 2001, pp. 10379-10386
A density functional theoretical study is presented, which implicates a nov
el S-3-cleavage in the decomposition of a pentathiepin. This study predicts
an interconversion between a pentathiepin and an open-chain polysulfur ion
intermediate from which a key determinant in the chemistry then follows. E
xpulsion of diatomic sulfur, S-2, is unlikely from the unimolecular collaps
e of the open-chain polysulfur ion. Instead, S-3 can dissociate due to an u
nusually long and weak sulfur-sulfur (S4-S5) bond. A mechanistic picture no
w emerges which predicts that the novel S-S cleavage reaction and the unant
icipated S3 fragmentation are a result of delocalization. of the negative c
harge within the remaining carbon-sulfur fragment. The computed results pre
sented here reveal a new aspect to the chemistry of pentathiepins, that of
S-3 unit transfer, which is proposed to have significance in the mechanism
of cytotoxicity of the natural product varacin, 1.