Natural macrocyclic molecules have a possible limited structural diversity.

This paper examines ring size patterns of natural product macrocycles. Evidence is presented that natural macrocycles containing 14-, 16-, and 18-membered rings are of frequent occurrence based on a data mining study. The results raise a question about the limited diversity of macrocycle ring sizes and the nature of the constraints that may cause them. The data suggest that the preference bears no relationship to the odd-even frequency in natural fatty acids. The trends reported here, along with those reported previously (Wessjohann et al. (2005) Mol Divers 9:171), may be generalized to better understand the possible structure preferences of natural macrocycles.

Implications for the existence of a heptasulfur linkage in natural o-benzopolysulfanes.

Natural o-benzopolysulfanes are often thought to exist as either the trisulfane or pentasulfane; the nomenclature has evolved around such notions. No study makes reference to the possible existence of natural o-benzoheptasulfanes. The work performed here indicates that a facile equilibration takes place between the tri-, penta-, and heptasulfanes (o-C(6)H(4)S(3), o-C(6)H(4)S(5), and o-C(6)H(4)S(7)) in solution. In these simpler (unnatural) compounds, the number of sulfur atoms can be established unequivocally from their independent syntheses. The o-benzopolysulfanes, even after purification, yield mixtures of compounds in solution. A similar equilibration may be anticipated for the corresponding natural products.

Generation of mono- and bis-dioxiranes from 2,3-butanedione.

Biacetyl reacts with oxone to give bis-dioxirane [3,3'-dimethyl-3,3'-bidioxirane, 3B] and mono-dioxirane [1-(3-methyl-dioxiran-3-yl)ethanone, 3A)]. Bis-dioxirane 3B is formed when two oxygens are incorporated into biacetyl, while mono-dioxirane 3A incorporated only one. A greater stability is observed in 3B compared to 3A, which is attributed to an alpha-dioxiranyl (anomeric) effect in the former. In contrast, 3A suffers from a destabilizing pi-electron withdrawing effect from the adjacent carbonyl group.

Substituent effects on the reactivity of benzo-1,2-dithiolan-3-one 1-oxides and their possible application to the synthesis of DNA-targeting drugs.

The efficiency of polysulfane product generation has been investigated for n-propyl thiol reactions with ortho- and para-substituted benzo-1,2-dithiolan-3-one 1-oxides in acetonitrile-water (7:3) mixtures. The reaction is facilitated by reducing the electron density at the para position or by placing substituents bearing lone pair electrons ortho to the dithiolanone-oxide (S1) reaction center. Through-space and through-bond effects both contribute to the conversion of polysulfane products.