Synthesis and kinetics of decomposition of some novel S-nitrosothiols

The S-nitrosothiols 2-acetamido-2-deoxy-S-nitroso-1-thio-beta-D-glucopyrano se 3,4,6-triacetate (GPSNO) and S-nitroso-N-carbamyl-D,L-penicillamine (SNC P) were synthesized by S-nitrosation of the corresponding thiols, isolated, and fully characterized. The nitrosothiol (TGSNO) from 1-thioglycerol was obtained as a red gelatinous liquid, which decomposed rapidly at room tempe rature and so was not characterized. The kinetics of decomposition of GPSNO showed that there is a surprisingly large thermal pathway overlaid with a Cu2+/RS- catalyzed reaction. The results strongly suggest that the product disulfide complexes Cu2+ (for which there is some spectral evidence), leadi ng to incomplete conversion by that route. Ascorbate also acts as a Cu2+ re ductant. Another S-nitroso sugar, S-nitroso-1-thio-beta-D-glucose (SNTG), b ehaved very similarly from solutions generated and used in situ. The decomp osition of TGSNO shows induction periods suggesting that slow initial gener ation of Cu+ (the true catalyst) is taking place. There appears to be also a significant alternative pathway (analogous to that found for GPSNO), wher e the rate appears to be independent of [Cu2+], but very unusually this pat hway is effectively halted by addition of EDTA either at the start of the r eaction or at a later time. Reaction schemes are put forward to account for these unusual reaction characteristics.