Discovery of rigid biphenyl Plasmodium falciparum DHFR inhibitors using a fragment linking strategy.

Plasmodium falciparum dihydrofolate reductase (PfDHFR), a historical target for antimalarials, has been considered compromised due to resistance inducing mutations caused by pyrimethamine (PYR) overexposure. The clinical candidate P218 has demonstrated that inhibitors could efficiently target both PYR-sensitive and PYR-resistant parasites through careful drug design. Yet, P218 clinical development has been limited by its pharmacokinetic profile, incompatible with single dose regimen. Herein, we report the design of new PfDHFR inhibitors using fragment-based design, aiming at improved lipophilicity and overall drug-like properties. Fragment-based screening identified hits binding in the pABA site of the enzyme. Using structure-guided design, hits were elaborated into leads by fragment linking with 2,4-diaminopyrimidine. Resulting compounds display nM range inhibition of both drug-sensitive and resistant PfDHFR, high selectivity against the human isoform, drug-like lipophilicity and metabolic stability. Compound 4 and its ester derivative 3 kill blood stage TM4/8.2 parasite at nM concentrations while showing no toxicity against Vero cells.

Benzothioate Glycoside from a terrestrial Streptomyces sp. TBRC 11511 from Thailand.

A new benzothioate glycoside metabolite, phitsanoside A, together with its new and known derivatives were isolated from Streptomyces sp. TBRC 11511 collected from sediment of a dry evergreen forest located in Phitsanulok Province, Thailand. The structure elucidation of the new compound was interpreted on the basis of spectroscopic data analysis. The configuration of the sugar moiety was derived based on NOESY nuclear magnetic resonance correlations, a vicinal coupling constant analysis, and the measurement of an optical rotation from the hydrolyzed sugar unit, which was identified as ß-D-glucopyranose. Phitsanoside A did not exhibit antibacterial activity against Bacillus cereus, Mycobacterium tuberculosis or Staphylococcus aureus, but phitsanoside B showed activity against all of them with MIC values of 3.13, 25 and 12.5 µg ml-1, respectively.

Antimicrobial and Cytotoxic Angucyclic Quinones from Actinomadura miaoliensis.

Eight new angucyclic quinones, miaosporones A to H (1-8), along with the previously described metabolites 8-hydroxy-3-methylbenz[a]anthraquinone (9), tetrangulol (10), 5,6-dihydro-1,8-dihydroxy-3-methybenz[a]anthracene-7,12-quinone (11), and SF2315A (12), were isolated from the terrestrial actinomycete Actinomadura miaoliensis TBRC 5172 obtained from sediment collected from the Huai Yang reservoir, Prachuap Khiri Khan Province, Thailand. The relative and absolute configurations of the new compounds were determined from analysis of NMR spectroscopic and X-ray crystallographic data. Miaosporone A exhibited antimalarial activity against Plasmodium falciparum K1 and antibacterial activity against Mycobacterium tuberculosis with respective IC50 values of 2.5 and 2.4 µM and displayed cytotoxic activities against both cancerous (MCF-7 and NCI-H187) and nonmalignant (Vero) cells.

Bioactive Dimeric Tetrahydroxanthones with 2,2'- and 4,4'-Axial Linkages from the Entomopathogenic Fungus Aschersonia confluens.

Thirteen tetrahydroxanthone dimers, atrop-ascherxanthone A (1), ascherxanthones C-G (2-6), and confluxanthones A-G (7-13), were isolated from the entomopathogenic fungus Aschersonia confluens BCC53152. The chemical structures were determined based on analysis of NMR spectroscopic and mass spectrometric data. The absolute configurations of compounds 1 and 7 were confirmed by single-crystal X-ray diffraction experiments, while the configurations of other compounds were assigned based upon evidence from NOESY and NOEDIFF experiments, modified Mosher's method, and ECD spectroscopic data together with biogenetic considerations. Compounds 1, 3-5, 7-11, and 13 showed antimalarial activity against Plasmodium falciparum (K1, multidrug-resistant strain) (IC50 0.6-6.1 µM), antitubercular activity against Mycobacterium tuberculosis H37Ra (MIC 6.3-25.0 µg/mL), and cytotoxicity against NCI-H187 (IC50 0.5-3.5 µM) and Vero (IC50 0.9-6.1 µM) cells. All tested compounds except for compound 9 exhibited cytotoxicity against KB cells (IC50 1.3-9.7 µM).

Secondary metabolites from cultures of the ant pathogenic fungus Ophiocordyceps irangiensis BCC 2728.

Five new compounds, iranginins A-E (1-5), together with sixteen known compounds were isolated from the insect pathogenic fungus Ophiocordyceps irangiensis BCC 2728. The structures and the absolute configurations of the new compounds were established by spectroscopic analyses, the application of modified Mosher's method (for 2), ECD calculation (for 5), and X-ray crystallographic analysis (for 4). LL-Z1640-5 and mucorisocoumarin C were active against Mycobacterium tuberculosis (MIC 41.7 and 85.0 µM, respectively), while peyroisocoumarin D exhibited cytotoxic activity (IC50 65.6 µM).

Chromanones and aryl glucoside analogs from the entomopathogenic fungus Aschersonia confluens BCC53152.

Six new compounds [ascherlactones A (1) and B (2), ascherchromanone A (3), phenethyl 4'-O-methylglucoside (8), 4'-O-methylpleoside (10), and 4'-O-methyltorachrysone 8-O-glucoside (11)] and one naturally new compound [4'-O-methyl-ß-d-benzylglucoside (9)] together with fourteen known compounds, including paecilodepsipeptides A (5), B (7), and D (4), conoideocrellide A (6), eugenin (12), 5-hydroxy-2,3-dimethyl-7-methoxychromone (13), (S)-1-phenyl-1,2-ethanediol (14), (2S)-l-3-phenyllactic acid (15), papuline [or (2S)-l-3-phenyllactic acid methyl ester, 16], 2'-epi terpendole A (17), terpendoles C (18) and D (19), cholic acid, and zeorin were isolated from the entomopathogenic fungus Aschersonia confluens BCC53152. Their chemical structures were elucidated on the basis of NMR spectroscopic and mass spectrometric analyses. The absolute configurations were determined by using the evidence from NOESY correlations, chemical means, optical rotation values together with comparison of ECD spectroscopic data with the calculated ECD spectra. The plausible biosynthetic pathway of compounds 1-3 was also proposed. Moreover, antimicrobial activity such as antimalarial, antitubercular, antifungal, and antibacterial activities and cytotoxicity against cancerous (MCF-7, KB, and NCI-H187) and non-cancerous (Vero) cells of the isolated compounds were evaluated.

6-Hydrophobic aromatic substituent pyrimethamine analogues as potential antimalarials for pyrimethamine-resistant Plasmodium falciparum.

The series of des-Cl (unsubstituted) and m-Cl phenyl analogues of PYR with various flexible 6-substituents were synthesized and studied for the binding affinities with highly resistant quadruple mutant (QM) DHFR. The derivatives carrying 4 atoms linker with a terminal carboxyl substituted on the aromatic ring exhibited good inhibition to the QM enzyme and also showed effective antimalarial activities against resistant P. falciparum bearing the mutant enzymes with relatively low cytotoxicity to mammalian cells. The X-ray crystallographic analysis of the enzyme-inhibitor complexes suggested that the hydrophobic substituent at 6-position was accommodated well in the hydrophobic pocket and the optimal length of the flexible linker could effectively promote the binding of the terminal carboxyl group to the key amino acid residues, Arg59 and Arg122.

Antimicrobial activity and cytotoxicity of xanthoquinodin analogs from the fungus Cytospora eugeniae BCC42696.

Eleven previously undescribed compounds, including cytosporanthraxanthone, xanthoquinodins A7-A10, ketoxanthoquinodin A6, xanthoquinodins B6-B8, and spiroxanthoquinodins A and B, and one synthetically known compound, 2-methoxy pinselin, as well as ten known compounds, including xanthoquinodins A4-A6, B4, and B5, chrysophanol, physcion, (4S)-5-hydroxy-4-methoxy-α-tetralone, (4S)-4,8-dihydroxy-α-tetralone (or isosclerone), and gonytolide C were isolated from the fungus Cytospora eugeniae BCC42696. Their chemical structures were determined based on the analysis of NMR spectroscopic and mass spectrometric data. Moreover, the absolute configurations of the unknown compounds were established by using NOESY and NOEDIFF NMR experiments along with CD spectroscopic data. The isolated xanthoquinodins exhibited a broad range of antimalarial, antibacterial, and fungicidal activities as well as cytotoxicity. Xanthoquinodins A6, B4, and B5 showed strong activity to Plasmodium falciparum, K1 strain (IC50 0.52-0.92 µM) and displayed anti-Bacillus cereus (MIC 1.56 µg/mL). Xanthoquinodin A6 also showed anti-Curvularia lunata (MIC 3.13 µg/mL). In addition, xanthoquinodins A4, A6, B4, and B5 and ketoxanthoquinodin A6 showed cytotoxicity against both cancerous (MCF-7, KB, NCI-H187) and non-cancerous (Vero) cells.