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J Alberto Marco

Publications and source records attributed to J Alberto Marco.

17 recordsLinked to original sources
PubMed2007

Stereoselective synthesis of the glycosidase inhibitor australine through a one-pot, double-cyclization strategy.

[reaction: see text] A stereocontrolled, convergent synthesis of the alkaloid australine, a glycosidase inhibitor of the pyrrolizidine class, is described. The chiral starting materials were ketone 3, derived from L-erythrulose, and alpha-alkoxy aldehyde 4, prepared from L-malic acid. A key step of the synthesis was the highly stereoselective aldol reaction between 4 and a Z boron enolate derived from 3. Another key step was the one-pot construction of the bicyclic pyrrolizidine system by means of a three-step sequence of SN2 displacements induced by benzylamine on a trimesylate precursor.

Aldehydes↗
PubMed2006

Stereoselective synthesis of the published structure of feigrisolide A. Structural revision of feigrisolides A and B.

The total synthesis of the proposed structure of feigrisolide A is reported. Ethyl (S)-3-hydroxybutyrate was the chiral starting material. A Brown asymmetric allylation and an Evans aldol reaction were key steps of the synthesis. The NMR data of the synthetic product are different from those of the natural product. The published structure of feigrisolide A is therefore erroneous. A subsequent comparison of spectral data strongly suggests that feigrisolides A and B are identical with (-)-nonactic acid and (+)-homononactic acid, respectively.

Anti-Bacterial Agents↗
PubMed2006

Stereoselective synthesis of the cytotoxic macrolide FD-891.

[reaction: see text] A total synthesis of the naturally occurring, cytotoxic macrolide FD-891 is described. Three fragments were first stereoselectively constructed using mainly asymmetric aldol and allylation reactions. The complete framework was then assembled using two Julia-Kocienski olefinations to connect the three fragments and a Yamaguchi reaction to close the macrolactone ring.

Antineoplastic Agents↗
PubMed2005

Stereoselective total synthesis and absolute configuration of the natural decanolides (-)-microcarpalide and (+)-lethaloxin. Identity of (+)-lethaloxin and (+)-pinolidoxin.

[reaction: see text] Convergent, stereoselective syntheses of the pharmacologically active, naturally occurring lactones (-)-microcarpalide and (+)-lethaloxin have been achieved from the commercially available, chiral reagents (R)-glycidol, (S,S)-tartaric acid, and d-ribose as the starting materials. These syntheses have further served to establish the hitherto unknown absolute configuration of (+)-lethaloxin and to show its identity with (+)-pinolidoxin.

Alkanes↗
PubMed2005

Double diastereoselection in aldol reactions mediated by dicyclohexylchloroborane between chiral aldehydes and a chiral ethyl ketone derived from L-erythrulose. synthesis of a C1-C9 fragment of the structure of the antifungal metabolite soraphen A1alpha.

[Chemical reaction: See text] Both matched and mismatched diastereoselections have been observed in the aldol reactions of a range of chiral aldehydes with the dicyclohexylboron enolate of a chiral ethyl ketone related to L-erythrulose. As was previously observed in the corresponding aldol reactions with L-erythrulose derivatives, the Felkin-Anh model provides an adequate explanation for the stereochemical outcome of reactions with chiral alpha-methyl aldehydes. However, a satisfactory account of the results observed with alpha-oxygenated aldehydes was only possible with the Cornforth model. As a practical application of the methodology described herein, a C1-C9 fragment of the structure of the antifungal macrolide soraphen A1alpha has been prepared in a convergent and stereoselective way.

Journal Article↗
PubMed2005

Stereoselective synthesis of the naturally occurring styryllactones (+)-goniofufurone and (+)-cardiobutanolide.

The naturally occurring gamma-lactones (+)-goniofufurone 1 and (+)-cardiobutanolide 2, two pharmacologically active products from Goniothalamus species (Annonaceae), have been synthesized in enantiopure form using l-erythrulose as the chiral starting material. Key steps of these syntheses were a stereoselective anti boron aldol reaction and an asymmetric allylboration.

4-Butyrolactone↗
PubMed2005

Sesquiterpenes from Centaurea aspera.

The aerial parts of two subspecies of Centaurea aspera L. (Asteraceae) yielded the germacranolides 1a-h, 2, 3, 4 and 5, the elemane derivatives 6d and 6f, the lignan matairesinol, the degraded terpene loliolide, and the onopordopicrin-valine dimeric adduct 7. From these, compounds 1e, 3 and 6d are natural products. The chemical composition of the two subspecies is very similar, a circumstance which does not support a taxonomic subdivision of the species.

Centaurea↗
PubMed2004

Stereoselective synthesis of the antiprotozoal lactone passifloricin A and seven isomers thereof.

The conjugated delta-lactone passifloricin A, a natural product with antiprotozoal activity, and seven isomers thereof have been synthesized in enantiopure form. It has been shown in this way that the proposed structure for the natural compound was erroneous. The correct structure is now evidenced. Key steps of the syntheses were asymmetric Brown-type aldehyde allylations and ring-closing metatheses.

Antiprotozoal Agents↗
PubMed2003

Double diastereoselection in aldol reactions mediated by dicyclohexylchloroborane between L-erythrulose derivatives and chiral aldehydes. The Felkin-Anh versus Cornforth dichotomy.

Both matched and mismatched diastereoselections have been observed in aldol reactions of the B,B-dicyclohexylboron enolate of a protected l-erythrulose derivative with a range of chiral aldehydes. The stereochemical outcome of reactions with alpha-methyl aldehydes can be adequately explained within the Felkin-Anh paradigm. In the case of alpha-oxygenated aldehydes, however, strict adherence to this model does not allow for a satisfactory account of the observed results. In such cases, the Cornforth model provides a much better explanation.

Journal Article↗
PubMed2003

Stereoselective synthesis and determination of the cytotoxic properties of spicigerolide and three of its stereoisomers.

Stereoselective syntheses of the naturally occurring, cytotoxic lactone spicigerolide and three nonnatural stereoisomers thereof are described. The commercially available sugar l-rhamnose was in all cases the chiral starting material. Key steps in each of these syntheses were asymmetric Brown allylations and ring-closing metatheses. The cytotoxic activities of the four lactones against a range of tumoral lines were then determined.

Antineoplastic Agents↗
PubMed2003

On the structure of passifloricin A: asymmetric synthesis of the delta-lactones of (2Z,5S,7R,9S,11S)- and (2Z,5R,7R,9S,11S)tetrahydroxyhexacos-2-enoic acid.

Stereoselective syntheses of the delta-lactone of (2Z,5S,7R,9S,11S)-tetrahydroxyhexacos-2-enoic acid, the structure reported for passifloricin A, and of its (5R)-epimer are described. The creation of all stereogenic centers relied upon Brown's asymmetric allylation methodology. The lactone ring was created via ring-closing metathesis. The NMR data of both synthetic products, however, were different from those of the natural product. The published structure of passifloricin A is thus erroneous and will require further synthetic work to be unambiguously assigned. [structure: see text]

Cyclization↗
PubMed2003

Tigliane diterpenes from the latex of Euphorbia obtusifolia with inhibitory activity on the mammalian mitochondrial respiratory chain.

Six diterpenes isolated from the latex of Euphorbia obtusifolia Poir. (Euphorbiaceae) were evaluated for their inhibition of the NADH oxidase activity in submitochondrial particles from beef heart. 4,20-Dideoxyphorbol-12,13-bis(isobutyrate) was the most potent inhibitor and showed an inhibitory concentration with IC(50) value of 2.6+/-0.3mM. In the present study, some structure-activity trends are suggested for the inhibitory activity of the mammalian mitochondrial respiratory chain of these natural product derivatives of 4-deoxyphorbol esters.

Animals↗
PubMed2003

Jatrophane diterpenes from the latex of Euphorbia obtusifolia with inhibitory activity on the mammalian mitochondrial respiratory chain.

Seven diterpenes isolated of the latex of the Euphorbia obtusifolia were evaluated as inhibitors of the NADH oxidase activity in submitochondrial particles from bovine heart. Compound 2, 2,3,5,7,8,9,15-heptahydroxyjatropha-6(17),11-diene-14-one 8,9-diacetate 7-isobutyrate 2,3-bis(2-methylbutyrate), was the most potent inhibitor with an inhibitory concentration (IC 50 ) value of 5.1 +/- 0.2 microM. In the present study, some structure-activity trends are suggested for the inhibitory activity of these natural products on the mammalian mitochondrial respiratory chain.

Animals↗
PubMed2002

Stereoselective synthesis of microcarpalide.

The first total synthesis of the naturally occurring nonenolide, microcarpalide, is described. The key step in the synthesis was the ring-closing metathesis of a dienic ester prepared in turn by coupling an acid and an alcohol stereoselectively synthesized from (S,S)-tartaric acid and (R)-glycidol, respectively. [structure: see text]

Alkanes↗
PubMed2002

Stereoselective synthesis of (+)-boronolide.

The delta-lactone boronolide (+)-1, a pharmacologically active, naturally occurring product, has been synthesized in enantiopure form with L-erythrulose as the chiral starting material. The key steps of the synthesis were a highly stereoselective aldol-reduction one-pot sequence, an indium-mediated diastereoselective aldehyde allylation, and a ring-closing metathesis.

Combinatorial Chemistry Techniques↗
PubMed2002

Silphinene sesquiterpenes as model insect antifeedants.

Silphinene sesquiterpenes are established chrysomelid antifeedants. In this work, nine silphinene analogs, 11beta-acetoxy-5alpha-angeloyloxysilphinen-3-one (1), 11beta-acetoxy-5alpha-tigloyloxysilphinen-3-one (2), 11beta-acetoxy-5alpha-isobutyryloxysilphinen-3-one (3), 11beta-hydroxy-5alpha-angeloyloxysilphinen-3-one (4), 11beta,5alpha-dihydroxysilphinen-3-one (5), 11beta,5alpha-diacetoxysilphinen-3-one (6), 5alpha,11beta-diisobutyryloxysilphinen-3-one (7), silphinen-3,5,11-trione (8), and O-methyl-5-epicantabrenolic acid methyl ester (10), and a presilphiperfolane sesquiterpene (9) were tested against several divergent insect species, including the lepidopteran Spodoptera littoralis, the chrysomelid Leptinotarsa decemlineata, and five aphid species, and their antifeedant effects were compared with those of picrotoxinin, a GABA-antagonist, and thymol, an allosteric modulator for insect GABA receptors. All insects tested responded to at least one silphinene analog and/or GABA antagonist. Compound 3 and thymol were effective antifeedants against all species tested except S. littoralis, with varying potencies according to their feeding ecologies. The toxicity of these compounds was species-dependent and did not correlate with their antifeedant effect.

Animals↗