S-Nitroso-N-acetylpenicillamine

S-Nitroso-N-acetylpenicillamine is the chemical compound with the formula ONSC(CH₃)₂CH(NHAc)CO₂H (Ac = acetyl). The molecule is an important donor of the NO⁺ in biochemistry. It has received much attention because nitric oxide and some organic nitroso derivatives serve as signaling molecules in living systems, especially related to vasodilation. SNAP is used as a model for the general class of S-nitrosothiols.^[1] S-Nitrosoglutathione is a related agent.

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Organic chemistry background

SNAP is derived from the amino acid penicillamine. The prefix "S" indicates that the NO group is attached to sulfur.

Nitrosothiols contain the RS-N=O functional group (R = alkyl, aryl). The S-N-O angle deviates strongly from 180° because the nitrogen atom bears of lone pair of electrons.

Thionitroso compounds arise from condensation from nitrous acid and a thiol:^[2]

RSH + HONO → RSNO + H₂O

Many other methods exist for their synthesis. Once formed, these deeply coloured compounds are often thermally unstable with respect to formation of the disulfide and nitric oxide.

SNAP releases NO⁺ upon treatment with acids:

RSNO + H⁺ → RSH + NO⁺

Thionitroso compounds transfer NO to other thiols:

RSNO + R'SH → RSH + R'SNO

References

1. ^ Zhang Y.; Hogg, N. “S-Nitrosothiols: cellular formation and transport” Free Radical Biology and Medicine 2005, volume 38, pp. 831-838. doi:10.1016/j.freeradbiomed.2004.12.016
2. ^ Wang, P. G.; Xian, M.; Tang, X.; Wu, X.; Wen, Z.; Cai, T.; Janczuk, A. J., "Nitric Oxide Donors: Chemical Activities and Biological Applications", Chemical Reviews, 2002, 102, 1091 - 1134.doi:10.1021/cr000040l