Synthesis of water soluble pentacyclic dihydroxyterpene carboxylic acid derivatives coupled amino acids and their inhibition activities on α-glucosidase.

Twenty maslinic acid and corosolic acid derivatives were obtained by coupling with l-amino acids at C-28 position. The α-glucosidase inhibitory activities of the present compounds were evaluated in vitro. Results reveal that some of the derivatives exhibit a better α-glucosidase inhibitory activity than that of acarbose in the test conditions of ethanol-water solution and DMSO. It is worth noting that maslinic acid and corosolic acid derivatives coupled aspartic acid (9f: IC50  = 382 μm and 10f: IC50  = 364 μm, respectively) have the best water solubility and thus presented higher inhibitory activity than that of acarbose (IC50  = 484 μm). Unfortunately, all of the derivatives possess lower inhibitory properties of α-glucosidase than those of the parent compounds in the measurement system of DMSO solution, even if the derivatives exhibit better water solubility than that of the parent compounds.