ABSTRACT
A 384-well microtitre plate fluorescence cleavage assay was developed to identify inhibitors of the cysteine protease falcipain-2, an important antimalarial drug target. Bioassay-guided isolation of a MeOH extract from a myxobacterium Chitinophaga sp. Y23 isolated from soil collected in Singapore, led to the identification of a new acyltetrapeptide, falcitidin (1), which displayed an IC50 value of 6 µM against falcipain-2. The planar structure of 1 was secured by NMR and MS/MS analysis. Attempts to isolate further material for biological testing were hampered by inconsistent production and by a low yield (<100 µg l(-1)). The absolute configuration of 1 was determined by Marfey's analysis and the structure was confirmed through total synthesis as isovaleric acid-D-His-L-Ile-L-Val-L-Pro-NH2. Falcitidin (1) is the first member of a new class of falcipain-2 inhibitors and, unlike other peptide-based inhibitors, does not contain reactive groups that irreversibly bind to active cysteine sites.
Subject(s)
Antimalarials/isolation & purification , Antimalarials/pharmacology , Cysteine Endopeptidases/metabolism , Oligopeptides/isolation & purification , Oligopeptides/pharmacology , Protease Inhibitors/isolation & purification , Protease Inhibitors/pharmacology , Antimalarials/chemical synthesis , Antimalarials/chemistry , Bacteroidetes/chemistry , Bacteroidetes/isolation & purification , Biological Assay , Drug Evaluation, Preclinical , Humans , Inhibitory Concentration 50 , Magnetic Resonance Spectroscopy , Molecular Structure , Oligopeptides/chemical synthesis , Oligopeptides/chemistry , Protease Inhibitors/chemical synthesis , Protease Inhibitors/chemistry , Singapore , Soil Microbiology , Tandem Mass SpectrometryABSTRACT
Bioassay-directed fractionation using a glucocorticoid receptor assay led to the isolation of two new, weakly active polyprenylated acylphloroglucinol derivatives, sundaicumones A (1) and B (2), from the leaves of Calophyllum sundaicum collected in Singapore. The structures of 1 and 2, which were established by spectroscopic methods, contain a 3-substituted hexanoic acid unit not previously reported in other polyprenylated acylphloroglucinols.
Subject(s)
Calophyllum/chemistry , Phloroglucinol , Plants, Medicinal/chemistry , Receptors, Glucocorticoid/antagonists & inhibitors , Humans , Molecular Structure , Phloroglucinol/analogs & derivatives , Phloroglucinol/chemistry , Phloroglucinol/isolation & purification , Phloroglucinol/pharmacology , Plant Leaves/chemistry , Singapore , Tumor Cells, CulturedABSTRACT
1D and 2D NMR techniques were used to assign fully the spectra of three aspidofractinine alkaloids, kopsine (1), fruticosamine (2) and fruticosine (3), isolated from a cultivated specimen of the plant Kopsia fruticosa (Apocynaceae). The assignment of the NMR data for 1, 2 and 3 will help in the future assignments of related alkaloids.
Subject(s)
Alkaloids/chemistry , Indole Alkaloids/chemistry , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Spectroscopy/standards , Alkaloids/isolation & purification , Indole Alkaloids/isolation & purification , Molecular Conformation , Reference StandardsABSTRACT
An extract from the fungus Emericella aurantiobrunnea was found to compete with macrophage inflammatory protein (MIP)-1alpha for binding to human CCR5 in a scintillation proximity assay (SPA). Bioassay-guided fractionation led to the isolation of variecolin (1) and variecolol (2), which had IC50 values of 9 and 32 microM, respectively. An X-ray crystal structure of variecolin (1) was obtained for the first time. Also isolated were four new inactive analogues, emericolin A (3), B (4), C (5), and D (6), and the relative stereochemistry of these compounds was determined by NMR methods using ROESY spectra and 1H/1H coupling constants.
