Diabetes mellitus (DM) is a complex disorder characterised by hyperglycaemia. It is primarily classified into insulin-dependent DM (type 1 diabetes), non-insulin-dependent DM (type 2 diabetes) and gestational diabetes. Type 2 diabetes is responsible for 85–95% of all diabete. Administration of an a-glucosidase inhibitor has been proposed as a treatment for DM type 2, since it works by preventing the digestion of carbohydrates. In fact, acarbose, known as an a-glucosidase inhibitor, has been shown to inhibit the increase in blood glucose level after meals. However, it also causes various side effects such as flatulence, diarrhoea and abdominal discomfort. Therefore, safer natural a-glucosidase inhibitors are essential for the treatment of type 2 diabetes.
Corosolic acid (2a,3b-dihydroxyurs-12-en-28-oic acid, 1) is the major pentacyclic triterpene in Banaba leaves (Lagerstroemia speciosa L.) which has been used as a traditional oriental medicine to treat diabetes, polyuria and polydipsia it is also abundant in Eriobotrya japonica and Weigela subsessilis . It is an interesting leading compound of versatile pharmacological activities, such as anti-diabetic, antiobesity, antioxidant, cytotoxicity, anti-inflammatory and anti-hypertensive. Due to such activities, the preparation of derivatives of corosolic acid for structure–activity relationship (SAR) studies has attracted recent attention, but the sites that can be modified by chemical procedures were limited to the activated position of the molecule.
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