Synthesis of the individual diastereomers of the cysteine conjugate of 3-mercaptohexanol (3-MH).

The individual diastereoisomers of the cysteine conjugate of 3-mercaptohexanol (4) were synthesized with high isomeric purity (>98%). On treatment with Apotryptophanase enzyme, the 3R diastereoisomer of 4 gave an 82% yield of the R enantiomer of 1, with no trace of the 3S enantiomer present. Conversely, the 3S diastereoisomer of 4 gave the 3S enantiomer of 1 (43%) accompanied by a trace of the 3R form (S/R = 98.

Micropatterning of porous silicon films by direct laser writing.

In this study, we demonstrate that porous silicon films can be ablated by the pulsed nitrogen laser of a commercial MALDI mass spectrometer. The extent of laser-induced ablation was found to depend on the doping level and surface chemistry of the porous silicon film. Using direct laser writing with or without a mask, micropatterns were generated on the porous silicon surface.

The regiochemistry of cyclization of alpha-sulfenyl-, alpha-sulfinyl-, and alpha-sulfonyl-5-hexenyl radicals: procedures leading to regioselective syntheses of cyclic sulfones and sulfoxides.

A study of the cyclization of alpha-sulfenyl-, alpha-sulfinyl-, and alpha-sulfonyl-5-hexenyl and 5-methyl-5-hexenyl radicals reveals a unique contrast in the mode of ring closure of the radicals. In the case of the 5-hexenyl radicals, the sulfinyl-substituted species displays unexpected regioselectivity relative to its analogues. Thus, while the alpha-S- and alpha-SO(2)-5-hexenyl radicals give measurable and increasing quantities of 6-endo product, the alpha-sulfinyl species cyclizes with high selectivity (95.

Regioselectivity of ring closure of 2-thia- and 2-sulfonyl-5-methyl-5-hexenyl radicals.

Ring closure of the alpha-substituted radicals 4 (X = S, SO(2)) is observed to be irreversible and to lead to significant amounts of the product of 6-endo cyclization. Indeed, reduction of the sulfonyl-based radical 4 (X = SO(2)), in which regioselectivity is believed to be controlled by a combination of both steric and FMO interactions, is found to provide an excellent route to the cyclic sulfone 7 (X = SO(2)) in high yield. [reaction: see text]