Isolation and synthesis of falcitidin, a novel myxobacterial-derived acyltetrapeptide with activity against the malaria target falcipain-2.

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.

Absolute configuration and total synthesis of a novel antimalarial lipopeptide by the de novo preparation of chiral nonproteinogenic amino acids.

The absolute configuration (via degradation and Marfey's derivatization studies) and the total synthesis of a novel antimalarial lipid-peptide isolated from Streptomyces sp. (IC(50) = 0.8 µM, Plasmodium falciparum 3D7) is disclosed. To this end, versatile stereocontrolled routes to nonproteinogenic amino acids (via catalytic Mannich, Sharpless methods) and enantiomeric trans fatty acids (via Evans alkylation, Kocienski-Julia olefination) have been developed.

Identification of a naturally occurring quinazolin-4(3H)-one firefly luciferase inhibitor.

A prefractionated Streptomyces-derived extract was initially identified as being active using a luciferase-based AMP-activated protein kinase (AMPK) assay. Bioassay-guided fractionation led to the isolation of the new compound quinazolin-4(3H)-one (1) as the active component. However, 1 was shown to have potent firefly luciferase inhibitory activity with no effect on AMPK. This is the first report of a natural luciferase inhibitor.

Naravelia zeylanica [corrected] occurrence of primary benzamides in flowering plants.

Extract of Naravelia zeylanica (Ranunculaceae) yielded three simple benzamides, 3,4-methylenedioxybenzamide, 4-methoxybenzamide and 4-hydroxy-3-methoxybenzamide. These simple C6C1 metabolites have been encountered as natural products for the first time. The compounds were identified by direct comparison of their spectral (1H- and 13C-NMR) and chromatographic (GCMS) data with those of authentic samples. Authentic 4-hydroxy-3-methoxybenzamide was synthesized in one step by treatment of 4-hydroxy-3-methoxybenzonitrile with sodium perborate. Authentic 3,4-methylenedioxybenzamide was synthesized from the corresponding acid.

Cyanohydrin glycosides of Passiflora: distribution pattern, a saturated cyclopentane derivative from P. guatemalensis, and formation of pseudocyanogenic alpha-hydroxyamides as isolation artefacts.

Nineteen species of Passiflora (Passifloraceae) were examined for the presence of cyanogenic glycosides. Passibiflorin, a bisglycoside containing the 6-deoxy-beta-D-gulopyranosyl residue, was isolated from P. apetala, P. biflora, P. cuneata, P. indecora, P. murucuja and P. perfoliata. In some cases this glycoside co-occurs with simple beta-D-glucopyranosides: tetraphyllin A, deidaclin, tetraphyllin B, volkenin, epivolkenin and taraktophyllin. P. citrina contains passicapsin, a rare glycoside with the 2,6-dideoxy-beta-D-xylo-hexopyranosyl moiety, while P. herbertiana contains tetraphyllin A, deidaclin, epivolkenin and taraktophyllin, P. discophora tetraphyllin B and volkenin, and P. x violacea tetraphyllin B sulfate. The remaining species were noncyanogenic. The glycosides were identified by 1H and 13C NMR spectroscopy following isolation by reversed-phase preparative HPLC. From P. guatemalensis, a new glucoside named passiguatemalin was isolated and identified as a 1-(beta-D-glucopyranosyloxy)-2,3-dihydroxycyclopentane-1-carbonitrile. An isomeric glycoside was prepared by catalytic hydrogenation of gynocardin. alpha-Hydroxyamides corresponding to the cyanogenic glycosides were isolated from several Passiflora species. These alpha-hydroxyamides, presumably formed during processing of the plant material, behave as cyanogenic compounds when treated with commercial Helix pomatia crude enzyme preparation. Thus, the enzyme preparation appears to contain an amide dehydratase, which converts alpha-hydroxyamides to cyanohydrins that liberate cyanide; this finding is of interest in connection with analysis of plant tissues and extracts using Helix pomatia enzymes.

Quinuclidinone O-Alkynyloximes with muscarinic agonist activity.

A series of quinuclidinone O-alkynyloximes (14-19) were synthesized and evaluated in radioligand displacement assays for binding affinities to M1-M3 muscarinic receptors. Radioligand displacement assays were carried out using [3H] oxotremorine-M and [3H] pirenzepine on rat cortical tissue and [3H] N-methylscopolamine on rat heart and submandibulary glands. Two alkynyloximes 15 and 18 had pirenzepine/oxotremorine M ratios which were indicative of muscarinic agonist and partial agonist activity, respectively. They were tested for their mnemonic effects in mice using the swimming escape task and found to attenuate scopolamine induced impairment of the task in mice at 2mg/kg. The results show that the O-alkynyloxime moiety linked to azacycles of appropriate size and rigidity (for example quinuclidine and tropane) is a potentially useful muscarinic pharmacophore that can be exploited for the design of muscarinic agonists.