Isolation, synthesis and photochemical properties of almazolone, a new indole alkaloid from a red alga of Senegal

An indole alkaloid bearing an oxazolone ring, christened almazolone, has been isolated from a new collection of Haraldiophyllum sp. from Dakar (Senegal), as an 88:12 mixture of (Z)/(E) stereoisomers. The relative ratio could be modified under controlled photochemical and thermal processes. The product (Z)-3-indolyl-2-(phenyl-propionylamino)-acrylic acid obtained by oxazolone ring opening has also been observed. Its formation has been confirmed by alkaline hydrolysis of (Z)-almazolone available from synthesis, where condensation of indole-3-carboxaldehyde with (3-phenylpropionylamino)-acetic acid represents the key step.