α-Glucosidase Inhibitors from Brickellia cavanillesii Sonia Escandó n-Rivera, † Martin Gonza ́ lez-Andrade, ‡ Robert Bye, § Edelmira Linares, § Andre ́ s Navarrete, † and Rachel Mata* ,† † Facultad de Química, Universidad Nacional Autó noma de Me ́ xico, Me ́ xico DF 04510, Mé xico ‡ Instituto Nacional de Medicina Genó mica, Secretaría de Salud, Me ́ xico DF 14610, Me ́ xico § Instituto de Biología, Universidad Nacional Autó noma de Me ́ xico, Me ́ xico DF 04510, Me ́ xico * S Supporting Information ABSTRACT: An aqueous extract from the aerial parts of Brickellia cavanillesii attenuated postprandial hyperglycemia in diabetic mice during oral glucose and sucrose tolerance tests. Experimental type-II DM was achieved by treating mice with streptozotocin (100 mg/kg) and β-nicotinamide adenine dinucleotide (40 mg/kg). These pharmacological results demonstrated that B. cavanillesii is effective for controlling fasting and postprandial blood glucose levels in animal models. The same aqueous extract also showed potent inhibitory activity (IC 50 = 0.169 vs 1.12 mg/mL for acarbose) against yeast α-glucosidase. Bioassay-guided fractionation of the active extract using the α-glucosidase inhibitory assay led to the isolation of several compounds including two chromenes [6-acetyl-5-hydroxy-2,2-dimethyl-2H-chromene (1) and 6- hydroxyacetyl-5-hydroxy-2,2-dimethyl-2H-chromene (2)], two sesquiterpene lactones [caleins B (3) and C (4)], several flavonoids [acacetin (5), genkwanin (6), isorhamnetin (7), kaempferol (8), and quercetin (9)], and 3,5-di-O-caffeoylquinic acid (10). Chromene 2 is a new chemical entity. Compounds 2, 4, 7, and 9 inhibited the activity of yeast α-glucosidase with IC 50 0.42, 0.28, 0.16, and 0.53 mM, respectively, vs 1.7 mM for acarbose. Kinetic analysis revealed that compounds 4 and 7 behaved as mixed-type inhibitors with K i values of 1.91 and 0.41 mM, respectively, while 2 was noncompetititive, with a K i of 0.13 mM. Docking analysis predicted that these compounds, except 2, bind to the enzyme at the catalytic site. Brickellia cavanillesii (Cass.) A. Gray (Asteraceae), commonly known as “prodigiosa” and “atanasia amarga”, is a bitter-tasting shrub widely distributed in Mexico. 1 Previous phytochemical studies of the aerial parts of this species resulted in the isolation and characterization of three flavonoids (brickellin, atanasin, and pendulin) 2-4 and 6-acetyl-5-hydroxy-2,2-dimethyl-2H- chromene (1). 5 This species, alone or in combination with other herbs, is widely commercialized in Mexico for the treatment of ulcers, dyspepsia, and diabetes. 1-6 According to a recent review, this is one of the 306 species most employed for the treatment of type-II diabetes mellitus (DM), 6 a chronic metabolic disease characterized by major imbalances in glucose metabolism and abnormalities in fat and protein metabolism. 7 About 246 million people suffer from type-II DM worldwide, and its incidence and serious complications continue to grow rapidly. Although there are several classes of antidiabetic drugs, achieving and maintaining long-term glycemia control is often challenging. In addition, many current agents have treatment- limiting side effects. 8 Therefore, there is an urgent need to find novel antidiabetic agents, including herbal remedies. 8 Thus, as part of our continuing efforts 9,10 to discover new therapies for treatment of diabetes derived from Mexican medicinal plants, the goals of the present study were to establish if B. cavanillesii had hypoglycemic activity and to identify new α-glucosidase inhibitors that could efficiently control postprandial glucose levels. ■ RESULTS AND DISCUSSION The use of B. cavanillensii in Mexican folk medicine prompted us to determine its efficacy as an antidiabetic agent using well- known animal models. First, an aqueous extract (56.2 and 316 mg/kg) of the aerial parts was tested using acute hypoglycemic as well as oral glucose and sucrose tolerance tests (OGTT and OSTT, respectively) in two sets of animals: normal and diabetic. Experimental type-II DM was achieved by treating mice with streptozotocin (STZ, 100 mg/kg) 15 min after an injection of β-nicotinamide adenine dinucleotide (NAD, 40 mg/kg). 10,11 This preliminary treatment with NAD provokes partial protection against the cytotoxic action of STZ by scavenging free radicals and causes only minor damage to pancreatic β-cell mass, creating a diabetic syndrome close to type-II DM. In the acute preliminary experiments, the aqueous extract decreased (p < 0.05) blood glucose levels in both normal (Table S1, Supporting Information) and NAD-STZ- diabetic mice (Figure 1) at doses of 100 and 316 mg/kg, an Received: March 15, 2012 Published: May 15, 2012 Article pubs.acs.org/jnp © 2012 American Chemical Society and American Society of Pharmacognosy 968 dx.doi.org/10.1021/np300204p | J. Nat. Prod. 2012, 75, 968-974