N-Acetyl-D-cysteine (NAC) is a derivative of the amino acid L-cysteine, specifically the D-enantiomer. Its chemical structure features a thiol (-SH) group and an acetylated amino group. It is a white to off-white crystalline powder. Its primary application is in biochemical and pharmaceutical research. As a derivative of D-cysteine, it serves as a key chiral building block for the synthesis of peptides and other bioactive molecules. It is also used as a precursor or intermediate in the preparation of various compounds where the D-configuration is required for specific biological activity or metabolic stability. In research settings, it can act as a thiol-modifying agent or a source of the D-cysteine moiety. While less common than its L-enantiomer (N-Acetyl-L-cysteine, a mucolytic agent and antioxidant), N-Acetyl-D-cysteine holds value in specialized synthetic and medicinal chemistry applications due to its chiral nature.