Curcumin–amino acid conjugates: Synthesis, antioxidant and antimutagenic attributes

Curcumin, a natural yellow colourant from turmeric, is insoluble in water. It has been rendered water-soluble by preparation of suitable amino acid derivatives. Several amino acid conjugates of curcumin were synthesised in high yields (45–76%). These curcumin derivatives were soluble in water at 1–10 mg/ml concentrations. Derivatives of curcumin with alkyl-substituted amino acids, such as alanine, valine, serine and cysteine, exhibited smaller IC50 values (∼50%) than did curcumin in antioxidant assays. With respect to antimutagenicity against Salmonella typhimurium TA 98 and TA 1531, the derivatives showed an effect stronger than or, in a few cases, similar to curcumin. These results clearly demonstrated that the conjugation of curcumin at the phenolic position with amino acids, while rendering the molecule water-soluble, led to the improvement of several of its in vitro biological attributes, the effect being more pronounced in the case of specific alkyl-substituted amino acids.