Investigation of some bioactive Thai medicinal plants

It has been estimated that plants are the most important source of medicine for more than 80% of the world’s population. Medicinal plants are a vital source of medication in developing countries. Despite the wealth of human experience and folklore concerning the medicinal uses of plants, proper scientific investigation has only been applied to a small fraction of the world’s plants. This is a cause of grave concern as plant species continue to disappear. A rapid response to this situation is urgently needed to prevent the disappearance of the plant species and the ethnopharmacological knowledge that accompanies them. In this review, recent work on the investigation of selected bioactive Thai medicinal plants is presented. Their biological activities against infectious diseases including antimalarial and anti-HIV, are highlighted, as well as their anticancer, antiulcer and anti-inflammatory properties. The chemical transformations of some selected compounds are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Isoquinoline derivatives as potential acetylcholinesterase inhibitors

Several bisbenzylisoquinoline alkaloid derivatives showed the inhibitory activity at acetylcholinesterase enzyme (AChE) in micromolar range. It is possible that monomeric moiety of bisbenzylisoquinoline alkaloid might be required for acetylcholinesterase enzyme inhibition. AChE inhibitory activity of related monomeric 1-benzylisoquinolines was examined by using Ellman colorimetric assay with galanthamine as a reference standard.     

Hybrid flavan-chalcones, aromatase and lipoxygenase inhibitors, from Desmos cochinchinensis

Hybrid flavan-chalcones, desmosflavans A (1) and B (2), together with three known compounds, cardamonin (3), pinocembrin (4) and chrysin (5), were isolated from leaves of Desmos cochinchinensis. Cardamonin (3) and chrysin (5) exhibited potent antioxidant activity with 15.0 and 12.2 ORAC units. Desmosflavans A (1) and B (2), pinocembrin (4), and chrysin (5) were found to be inhibitors of aromatase with respective IC₅₀ values of 1.8, 3.3, 0.9, and 0.8 μM. Desmosflavan A (1) inhibited lipoxygenase with the IC₅₀ value of 4.4 μM. Desmosflavan A (1) exhibited cytotoxic activity with IC₅₀ values of 0.29–3.75 μg/mL, while desmosflavan B (2) showed IC₅₀ values of 1.71–27.0 μg/mL.     

Pyranocoumarins from the twigs of Mammea siamensis

Four unusual pyranocoumarins (1-4) have been isolated from the dried twigs of M. siamensis. The structures were determined by spectroscopic data, especially 1D and 2D NMR experiments.     

Superbanone,A New 2‐Aryl‐3‐benzofuranone and Other Bioactive Constituents from the Tube Roots of Butea superba

Phytochemical investigation from the tube roots of Butea superba, led to the isolation and identification of a new 2‐aryl‐3‐benzofuranone named superbanone ( 1 ), one benzoin, 2‐hydroxy‐1‐(2‐hydroxy‐4‐methoxyphenyl)‐2‐(4‐methoxyphenyl)ethanone ( 2 ), eight pterocarpans ( 3  –  10 ), and eleven isoflavonoids ( 11  –  21 ). Compound 2 was identified for the first time as a natural product. The structure of the isolated compounds was elucidated using spectroscopic methods, mainly 1D‐ and 2D‐NMR. The isolated compounds and their derivatives were evaluated for α‐glucosidase inhibitory and antimalarial activities. Compounds 3 , 7 , 8 , and 11 showed promising α‐glucosidase inhibitory activity (IC₅₀ = 13.71 ± 0.54, 23.54 ± 0.75, 28.83 ± 1.02, and 12.35 ± 0.36 μm , respectively). Compounds 3 and 11 were twofold less active than the standard drug acarbose (IC₅₀ = 6.54 ± 0.04 μm ). None of the tested compounds was found to be active against Plasmodium falciparum strain 94. On the basis of biological activity results, structure–activity relationships are discussed.