Synthesis and characterization of a series of novel monoacylated ascorbic acid derivatives, 6-O-acyl-2-O-α-D-glucopyranosyl-l-ascorbic acids, as skin antioxidants

A series of novel monoacylated vitamin C derivatives were chemically synthesized with a stable ascorbate derivative, 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G), and acid anhydrides in pyridine. Their solubility in organic phase, thermal stability, radical scavenging activity, and in vitro skin permeability was evaluated. These monoacylated derivatives were identified as 6-O-acyl-2-O-α-D-glucopyranosyl-L-ascorbic acids (6-Acyl-AA-2G) by UV spectra, elemental analyses, and nuclear magnetic resonance spectroscopy. The reactions afforded 6-Acyl-AA-2G in high yields (30-60%). 6-Acyl-AA-2G exhibited satisfactory stability in neutral solution comparable to that of a typical stable derivative, AA-2G, and also showed the radical scavenging activity. The lipid solubility of 6-Acyl-AA-2G was increased with increasing length of their acyl group. Increased skin permeability was superior to those of AA-2G and ascorbic acid (AsA). 6-Acyl-AA-2G that is susceptible to enzymatic hydrolysis by tissue esterase and/or α-glucosidase produces AA-2G and AsA, which is in the skin tissues. Thus, these findings indicate that the novel vitamin C derivatives presented here, 6-Acyl-AA-2G, may be effective antioxidants in skin care and medicinal use.