C4H9NO2S
# C4H9NO2S

The molecular formula $C_4H_9NO_2S$ may refer to:

* Homocysteine, a non-proteinogenic α-amino acid
* S-Methylcysteine, amino acid with the nominal formula $CH_3SCH_2CH(NH_2)CO_2H;$ the S-methylated derivative of cysteine
