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 isolat ed from the stem bark of Avicennia alba (Avicenniaceae) collected in Singap ore, and their structures were elucidated by means of spectral methods. Gil lan and co-workers have proposed that the structures of the new phytoalexin s isolated from Avicennia marina are 1,2-naphthoquinones 8 and 9, Our synth etic and spectrometric studies showed that these structures should be revis ed respectively to 1,4-naphthoquinones 2 and 3, named avicequinone-B and -C by us.