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Two novel diarylheptanoids named katsumadain A (1) and katsumadain B (2) were isolated from the seeds of Alpinia katsumadai, and their structures were determined by spectroscopic analysis. Both katsumadains A (1) and B (2) showed anti-emetic activities on copper sulfate-induced emesis in young chicks.
The new compound, asperic acid (1), and the known compounds hexylitaconic acid (2), malformin C (3), pyrophen (4), and asperazine (5) were isolated from the saltwater culture of Aspergillus niger derived from a Caribbean sponge, Hyrtios proteus. The structure elucidation of asperic acid is presented.
Two new naphthopyrones, euplectin (1) and coneuplectin (2), have been isolated from the lichen Flavoparmelia euplecta and their structures elucidated using multidimensional NMR spectroscopic methods, including highfield (600 MHz) gHMBC and gNOE experiments. Cytotoxicity of the more abundant naphthopyrone (1) against the murine P-815 mastocytoma cell line (IC(50) ca. 1.67 microg/mL) has also been evaluated. These compounds are the first lichen metabolites known to contain indenone or indanone moieties in their structure. F. euplecta was also found to contain the known metabolites usnic acid, protocetraric acid, and skyrin.
The dichloromethane extract of Talaromyces convolutus cultivated on barley exhibited antifungal activity against Candida albicans. In the course of a search for the active compounds, four new tetramic acid derivatives, talaroconvolutins A (1), B (2), C (3), and D (4), were isolated along with ZG-1494alpha (5), and mitorubrin derivatives. The structures of talaroconvolutins A-D (1-4) were established on the basis of spectroscopic and chemical investigations and chemical correlations. The antifungal activity of the talaroconvolutins against the pathogenic fungi Aspergillus fumigates, Aspergillus niger, C. albicans, and Cryptococcus neoformans was determined.
The acetone extract of Nepeta caesarea yielded four new nepetalic acid derivatives, 3'alpha-[beta-sitosteryl-3beta-oxy]dihydronepetalactone (1), 3'beta-[5alpha-stigmast-7-ene-3beta-oxy]dihydronepetalact one (2), 3'alpha-[olean-12-ene-28-oyl-3beta-oxy]dihydronepetalactone (3), and 3'alpha-[lup-20(29)-ene-28-ol-3beta-oxy]dihydronepetalactone (4). The structures were elucidated by NMR and MS techniques.
Bioactivity-directed fractionation of the fermentation broth and mycelium of the coprophilous fungus Guanomyces polythrix led to the isolation of several phytotoxic compounds, including five new naphthopyranone derivatives (1-5). In addition, rubrofusarin B, emodin, citrinin, and 4-hydroxybenzoic acid methyl ester were obtained. The structures of the new compounds were established by spectral and chiroptical methods. The isolates caused significant inhibition of radicle growth of two weed seedlings (Amaranthus hypochondriacus and Echinochloa crusgalli) and interacted with both spinach and bovine brain calmodulins.
A new pyranone, 5-hydroxy-3-methoxy-4H-pyran-4-one (1), was isolated from the aerial parts of the desert shrub Haloxylon salicornicum. The structure was elucidated by X-ray structural analysis, NMR spectroscopy, and mass spectrometry. The monoacetate was also prepared, and molecular modeling studies and full NMR data were recorded.
Cultures of endophytic fungi collected in the Guanacaste Conservation Area of Costa Rica were screened for antifungal activity. CR377, a new pentaketide antifungal agent, was isolated from the culture broth of a fungus, CR377 (Fusarium sp.), that showed potent activity against Candida albicans in this assay. The structure of CR377 was established using 1- and 2-D NMR and HRFABMS.
[reaction--see text] An asymmetric total synthesis of the unusual siphonariid metabolite, (-)-baconipyrone C (3), is described. Key steps included a tin(II)-mediated aldol coupling for the preparation of the carboxylic acid 17 and two different boron-mediated aldol additions leading to alcohol 8. Ester formation using modified Yamaguchi conditions gave 24, leading on PMB deprotection to (-)-baconipyrone C.
A flexible enantioselective route to highly functionalized alpha, beta-unsaturated delta-lactones has allowed for the syntheses of the styryllactones: isoaltholactone, 3-epi-altholactone, and 5-hydroxygoniothalamin in 10%, 5%, and 13% overall yields from furfural, respectively. This approach derives its asymmetry by applying the Sharpless catalytic asymmetric dihydroxylation to vinylfuran. The resulting diols are produced in high enantioexcess and can be stereoselectively transformed into alpha,beta-unsaturated delta-lactones via a short highly diastereoselective oxidation and reduction sequence.
[figure: see text] The synthesis of the cyclohexan subunit of the siphonarlid metabolites baconipyrones A and B from furan is described. A key step included the alkylative ring opening of 7-oxanorbornenic sulfone 4 and oxidative desulfonylation of compound 8.
[reaction--see text] Each of four diastereomers of structure 2, corresponding to the lipophilic side chain of scyphostatin (1), were prepared. Careful analysis of their NMR spectral data and comparison with those of the natural product corroborates the recently reported (Org. Lett. 2000, 2, 505) stereochemical assignment. A strategy for the stereoselective synthesis of 2 has been achieved.
[figure: see text] This first asymmetric synthesis of enantiopure desacetylumuravumbolide and umuravumbolide via asymmetric reduction, allylboration, and ring-closing metathesis confirms their revised structures and configurations. A convenient procedure to upgrade the enantiopurity of alpha,beta-acetylenic alcohols is also described.
[structure] The deracemization of 3-nonyl-3,4-epoxybut-1-ene with Pd(0) in the presence of chiral ligands using p-methoxybenzyl alcohol as a nucleophile proceeds regio- and enantioselectively to form the monoprotected vinylglycidol in 99% ee. This chiral building block was converted in seven steps to (-)-malyngolide, an antibiotic showing significant activity against Mycobacterium smegmatis and Streptococcus pyogenes. An interesting aspect involves controlling the diastereoselectivity of protonation of an enolate via a distal hydroxyl group.
[figure: see text] Three diastereomers of membrenone-C were separately prepared using a common two directional chain extending synthetic strategy. This has established the absolute and relative configuration of the natural product to be as shown in the foregoing graphic. Key steps in the synthesis of all the isomers are a stereoselective aldol coupling and reduction giving the C7-C9 stereocenters, a two direction chain extending double titanium aldol coupling, and the trifluoroacetic acid promoted double cyclization/dehydration giving the two dihydropyrone rings.
[structure: see text]. The solution structure of (+)-discodermolide (1) has been determined via 1- and 2-D NMR techniques in conjunction with Monte Carlo conformational analysis. Taken together, the results demonstrate that in solution (+)-discodermolide occupies a helical conformation remarkably similar to the solid state conformation.
[structure: see text] Total synthesis of nafuredin, a selective NADH-fumarate reductase inhibitor, has been accomplished by a convergent approach. The C1-C8 and C9-C18 segments were derived efficiently from D-glucose and (S)-(-)-2-methyl-1-butanol, respectively, coupled by stereoselective Julia olefination, and converted to nafuredin.
[reaction: see text]. Total synthesis of the immunosuppresant pironetin has been achieved by a synthetic route in which the connections between starting materials and the desired structure are readily discerned. Key steps include a diastereoselective Lewis acid mediated crotylstannane aldehyde addition, a highly selective Lewis acid promoted Mukaiyama aldol reaction, an anti-selective SmI2 reduction of a beta-hydroxyketone, and finally a lactone annulation reaction.