2008 年 82 巻 3 号 p. 151-160
L-Ascorbic acid (AsA), vitamin C, possesses many biological activities, but it readily decomposes upon exposure to heat, UV light, metal ions, and oxidants. Therefore, Yamamoto and Muto et al. have developed a stable AsA derivative, 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G). AA-2G has been approved by the Japanese Government as a quasi-drug principal ingredient in skin care and as a food additive and is currently being used as a medical additive in commercial cosmetics. This stable AsA derivative exhibits vitamin C activity in vitro and in vivo after enzymatic hydrolysis to AsA by α-glucosidase. Recently, we have synthesized two types of monoacylated derivatives of AA-2G, 6-O-acyl-2-O-α-D-glucopyranosyl-L-ascorbic acids having a straight-acyl chain (6-sAcyl-AA-2G) and a branched-acyl chain (6-bAcyl-AA-2G), in order to improve the bioavailability of AA-2G. These derivatives showed satisfactory stability in neutral solution comparable to that of AA-2G, and had radical scavenging activity per se. The lipophilicity of 6-sAcyl- and 6-bAcyl-AA-2G was increased with increasing length of their acyl group. 6-sAcyl- and 6-bAcyl-AA-2G with an appropriate length of the acyl chain group exhibited antiscorbutic activity in guinea pigs and skin permeability superior to that of AA-2G in a human living skin equivalent model. At a lower concentration than AA-2G, 6-sAcyl- and 6-bAcyl-AA-2G enhanced both dibutyryl cyclic AMP- and nerve growth factor-induced neurite outgrowth in PC 12 cells, antigen-specific antibody production in murine splenic cells and collagen synthesis in human skin fibroblasts, and inhibited melanogenesis in B16 mouse melanoma cells. It is necessary to metabolize the derivatives by α-glucosidase at least to demonstrate these biological activities. These results indicate that 6-sAcyl- and 6-bAcyl-AA-2G are readily available sources of AsA activity in vitro and in vivo, may be useful as an effective pharmacological agent and as a promising food additive.