A new anthraquinone (3,8-dihydroxy-2-methyl anthraquinone), named tectone (1), along with fourteen known compounds (2-15) comprised of five terpenoids (2-5, 15), four flavonoids (6-9), three flavone glycosides (10-12), and two phenolic glycosides (13-14) were isolated from the chloroform and n-butanol fractions of the ethanol extract of Tectona grandis leaves. Attempts were made to synthesize compound 1. This resulted in the synthesis of three additional anthraquinones (16-18), out of which compound 16 is new. The structures of all compounds were established by spectral analysis. The isolated and synthesized compounds were evaluated for their antihyperglycemic activity. Compounds 1, 2, 4 and 14 showed significant antihyperglycemic activity in streptozotocin-induced diabetic rats at a dose of 100 mg/kg body weight, which is comparable to the standard drug metformin.