Three novel and one new lignan, chamaecypanones A, B, obtulignolide and isootobanone from the heartwood of Chamaecyparis obtusa var. formosana

Three novel lignans, chamaecypanone A 1, chamaecypanone B 2, obtulignolide 4, and one new lignan, isootobanone 3, were isolated from the heartwood of Chamaecyparis obtusa var. formosana, and were elucidated on the basis of 2D NMR techniques. Compounds 1 and 2, derived from a phenyltetrahydronaphthalene-type lignan by cleavage and cyclization, are anthrone derivatives. Compound 3 is a phenyltetrahydronaphthalene-type lignan, and 4 is a 3,4-secophenyltetrahydronaphthalene-type lignan. The absolute configurations of 3 and otobanone 5 were elucidated by a modified Mosherʹs method.