Blepharocalyxins C−E, Three New Dimeric Diarylheptanoids, and Related Compounds from the Seeds of Alpinia blepharocalyx

Three novel diarylheptanoids, blepharocalyxins C−E (5−7), together with four new (1−4) and one known (8) diarylheptanoids bearing a tetrahydropyran ring were isolated from the residual fraction of an EtOH extract of the seeds of Alpinia blepharocalyx. The structures and the stereochemistry at the chiral centers of the new diarylheptanoids were elucidated by spectroscopic techniques including 2D NMR spectroscopy. Blepharocalyxins C−E (5−7) have a novel carbon framework and are dimeric diarylheptanoids consisting of two diarylheptanoid units. Blepharocalyxin D (6) showed potent antiproliferative activity against murine colon 26-L5 carcinoma cells (ED50, 3.61 μM), while against human HT-1080 fibrosarcoma cells, blepharocalyxin E (7) showed potent activity (ED50, 9.02 μM).