Chemical Constituents of Avicennia alba. Isolation and Structural Elucidation of New Naphthoquinones and Their Analogues

Three new naphthoquinones and their analogues, named avicequinone-A (1), -B (2), -C (3), and avicenol-A (4), -B (5), -C (6), respectively, were isolated from the stem bark of Avicennia alba (Avicenniaceae) collected in Singapore, and their structures were elucidated by means of spectral methods.Gillan and co-workers have proposed that the structures of the new phytoalexins isolated from Avicennia marina are 1, 2-naphthoquinones 8 and 9. Our synthetic and spectrometric studies showed that these structures should be revised respectively to 1, 4-naphthoquinones 2 and 3, named avicequinone-B and -C by us.