Guided by brine shrimp toxicity and human tumor cell toxicity, fractionation of the alcoholic extract from the stem bark of Goniothalamus marcanii led to the isolation of four new 1-azaanthraquinones: marcanines B (3), C (4), D (5), and E (6), along with two known derivatives: marcanine A and dielsiquinone. A new 5-hydroxy-3-amino-2-aceto-1,4-naphthoquinone (7), a possible 1-azaanthraquinone biosynthetic precursor, was also isolated. The structures of the compounds were elucidated by spectroscopic analyses, mainly 1D and 2D NMR techniques ((1)H, (13)C, NOEDS, COSY, HMQC, and HMBC), as well as comparison with literature data. All the compounds except 6 were evaluated for cytotoxic activity. They exhibited significant cytotoxicity against several human tumor cell lines, A-549, HT-29, MCF7, RPMI, and U251 with the ED(50) in the range of 0.04-3.03 microM.

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Four additional new bioactive heptenes, melodorinol [2], homomelodienone [4], 7-hydroxy-6-hydromelodienone [5], and homoisomelodienone [7] have been isolated from Melodorum fruticosum. These compounds were slightly to significantly cytotoxic to human tumor cell lines. Their structures have been determined by comparison of their 1H-nmr, 13C-nmr, and mass spectral data with those of prototype compounds (acetylmelodorinol [1], melodienone 3, and isomelodienone [6]).

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A novel 3'',4''-dihydroglabridin was successfully prepared for studying on tyrosinase inhibitory activity. The result demonstrated that 3'',4''-dihydroglabridin exhibited higher activity than glabridin (IC(50) value = 11.40 microM), which is probably due to the 4-substituted resorcinol skeleton and the lacking of double bond between carbon atom 3'' and 4'' on its structure giving more conformational flexibily to interact with the enzyme more effectively. In addition, various acylated derivatives were synthesized as glabridin prodrugs. The chemical and enzymatic hydrolysis of prodrugs revealed that the diacetate ester was rapidly hydrolyzed by porcine liver esterase with the half-life of 2.36 minute, while those of the dihexanoate was 14.8 hour. Both of them were sufficiently stable in phosphate buffer, both pH 5.5 and 7.4, at 37 degrees C with more than 15 days half-life.

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