New Lamellarin Alkaloids from the Indian Ascidian Didemnum obscurum and Their Antioxidant Properties

Three new lamellarin alkaloids, lamellarins γ (1), α (2), and ε (3), along with eight known lamellarin alkaloids, lamellarins M (4), K (5), K-diacetate (6), K-triacetate (7), U (8), I (9), C-diacetate (10), and X-triacetate (11), have been isolated from the Indian ascidian Didemnum obscurum. The structures of 111 were established using standard spectroscopic techniques. The structure of lamellarin K-triacetate (7) was further confirmed by X-ray crystallographic analysis. The antioxidant properties of lamellarin γ, lamellarin γ-monoacetate, lamellarins K, U, and I, and lamellarin C-diacetate were evaluated.