Acetylcholinesterase-inhibiting activity of marinoquinoline A (1), a new pyrroloquinoline from a novel species of a marine gliding bacterium Rapidithrix thailandica, was assessed (IC 50 4.9 μM). Two related pyrrole derivatives, 3-(2'-aminophenyl)-pyrrole (3) and 2,2-dimethyl-pyrrolo-1,2-dihydroquinoline (4), were also isolated from two other strains of R. thailandica. The isolation of 3 from a natural source is reported here for the first time. Compound 4 was proposed to be an isolation artifact derived from 3.The two isolated compounds were virtually inactive in the acetylcholinesterase-inhibitory assay (enzyme inhibition < 30% at 0.1 g L -1 ).

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For the purpose of discovering anti-HIV-1 agents from natural sources, water and EtOH extracts of 50 Thai plants were screened for their inhibitory activity against HIV-1 integrase (IN), an enzyme essential for viral replication. Of these plants, an EtOH extract of Coleus parvifolius Benth. (aerial parts) showed potent activity against HIV-1 IN with an IC50 value of 9.2 microg/mL. From this extract, 11 compounds were isolated and identified as luteolin 5-O-beta-d-glucopyranoside (1), luteolin (2), luteolin 7-methyl ether (3), luteolin 5-O-beta-d-glucuronide (4), 5-O-beta-d-glucopyranosyl-luteolin 7-methyl ether (5), rosmarinic acid (6), rosmarinic acid methyl ester (7), daucosterol (8), a mixture of alpha- and beta-amyrin (9, 10) and phytol (11). Of these compounds, rosmarinic acid methyl ester (7), rosmarinic acid (6), luteolin (2) and luteolin 7-methyl ether (3) exhibited inhibitory activities against HIV-1 IN with IC50 values of 3.1, 5.0, 11.0 and 11.0 microM, respectively. Among rosmarinic acid derivatives, the HIV-1 IN inhibitory activity increased in turn for a dimer (IC50 = 5.0 microM), a trimer (IC50 = 1.4 microM), and a tetramer (IC50 = 1.0 microM).

Acetylcholinesterase (AChE) inhibitors have lately gained interest as potential drugs in the treatment of Alzheimer's disease. Three AChE inhibitors were isolated from tubers of a Thai medicinal plant, Stephania venosa (Bl) Spreng. They were identified as quaternary protoberberine alkaloids, stepharanine, cyclanoline and N-methyl stepholidine. They expressed inhibitory activity on AChE with IC50 values (concentration that caused 50% inhibition of activity) of 14.10 +/- 0.81, 9.23 +/- 3.47 and 31.30 +/- 3.67 microM, respectively. The AChE inhibitory activity of these compounds was compared with those of the related compounds, palmatine, jatrorrhizine and berberine, as well as tertiary protoberberine alkaloids isolated from the same plant, stepholidine and corydalmine. The results suggest that the positive charge at the nitrogen of the tetrahydroisoquinoline portion, steric substitution at the nitrogen, planarity of the molecule or substitutions at C-2, -3, -9, and -10 affect the AChE inhibitory activity of protoberberine alkaloids.

A new scalarane-type sesterterpene, 12-deacetoxyscalarin 19-acetate (2), and two naturally new derivatives of manoalide-type sesterterpenes, (E)- and (Z)-neomanoalide 24,25-diacetates (3 and 4), were isolated from the Thai sponge Brachiaster sp., along with five other known sesterterpenes: heteronemin (1), heteronemin acetate (5), 12-epi-19-deoxyscalarin (6), 12-deacetyl-12-epi-19-deoxyscalarin (7), and manoalide 25-acetate (8). The antitubercular and cytotoxic activities of all eight compounds were evaluated to reveal the potent activity of compounds 1, 2, 5, and 8. Among these, compound 2 showed an interesting bioactivity profile, in possessing potent antitubercular activity and being practically inactive in the cytotoxicity bioassay.

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A new isonitrile diterpene of the amphilectane family, 8-isocyanoamphilecta-11(20),15-diene (4), was isolated from the sponge Ciocalapata sp., along with three known isonitriles, 8,15-diisocyano-11(20)-amphilectene (1), 7-isocyanoamphilecta-11(20),15-diene (2), and 8-isocyanoamphilecta-11(20),14-diene (3), and two steroidal peroxides, ergosterol peroxide (5) and 5α,9α-epidioxy-8α,14α-epoxy-(22E)-ergosta-6,22-dien-3β-ol (6). The structure of the new isonitrile was elucidated spectroscopically. In addition, anomalous multiplicities in the NMR spectra of some isolated isonitriles were observed and are reported here. The four isonitriles were strongly active against Plasmodium falciparum K1 with IC50 in a range of 0.09–1.07 μmol/L. Except for 1, which was cytotoxic against both MCF-7 and fibroblast cell lines, the other three diterpenes showed no significant cytotoxicity against either targeted cell lines. On the other hand, the steroidal peroxides 5 and 6, which were less active in the antimalarial bioassay (IC50 values of 6.28 and 7.13 µmol/L, respectively), were strongly cytotoxic against MCF-7 (IC50 values of 0.025 and 0.003 µmol/L, respectively), with very little toxicity against human fibroblasts.