0000000000022281
AUTHOR
J. Alberto Marco
showing 81 related works from this author
Sesquiterpene lactones and lignans from Artemisia arborescens
1997
The aerial parts of Artemisia arborescens yielded, in addition to several known compounds, a new guaianolide, a new homoditerpene endoperoxide, a new lignan of the sesamin type and a new azulene derivative.
Stereoselective Synthesis of Microcarpalide
2002
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]
Stereoselective Synthesis of (+)-Boronolide
2002
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.
Analysis of Rabbit Vascular Responses to DBI, an Ingol Derivative Isolated from Euphorbia canariensis
1997
Abstract We have analysed the effects of 7,12-O-diacetyl-8-O-benzoil-2,3-diepiingol (DBI), an ingol derivative isolated from E. canariensis, on isometric tension developed by isolated rabbit basilar and carotid arteries. Concentration-response curves to DBI (10−8 - 3 × 10−5 m) were obtained cumulatively in both arteries at resting tension and active tone (KC1, 50 mm). At resting tension, DBI induced a concentration-dependent contraction, which was not inhibited in Ca2+-free medium. H7 (1-(5-isoquinoline sulphonyl)-2-methylpiperazine dichloride) (10−4 m) inhibited the DBI-induced contraction both in basilar and in carotid arteries. Calmidazolium (10−4 m) inhibited the maximum contraction of …
Sesquiterpene lactones from iranian Artemisia species
1993
Abstract The aerial parts of Artemisia turcomanica and A. deserti yielded two new germacranolides, a new guaianolide, and several known mono- and sesquiterpenes.
Double Diastereoselection in Aldol Reactions Mediated by Dicyclohexylchloroborane between Chiral Aldehydes and a Chiral Ethyl Ketone Derived from l-E…
2005
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 α-methyl aldehydes. However, a satisfactory account of the results observed with α-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 A1α…
13C NMR spectra of eudesmane derivatives
1992
The 13C NMR spectral data of 18 eudesmane derivatives, mainly acids and esters of natural and synthetic origin, are reported, and the γ-effect of the epoxide ring in two diastereoisomeric epoxy esters is discussed.
Sesquiterpene lactones, waxes and volatile compounds from Artemisia herba-alba subspecies Valentina
1979
Abstract The structures of two sesquiterpene lactones isolated from Artemisia herba-alba subsp. valentina have been determined by spectroscopic methods. One of these was dihydroreynosin, the other was a new compound assigned the name torrentin. The chemical compositions of a wax and a hydrocarbon fraction from the essential oil have also been investigated.
Jatrophane derivatives and a rearranged jatrophane from Euphorbia terracina
1998
Abstract The aerial parts of Euphorbia terracina yielded 11 new jatrophane derivatives as well as a further diterpene displaying the novel 1(15 → 14) abeo -jatrophane framework.
Sesquiterpene lactones and dihydroflavonols from Andryala and Urospermum species
1994
Abstract The aerial parts of two Andryala species yielded several guaianolides and guaianolide glycosides, three of them being new. The aerial parts of Urospermum dalechampii yielded several known germacranolides and the new dihydroflavonol 3- O -methyltaxifolin.
Sesquiterpene lactones from Artemisia hispanica
1989
Abstract Extraction of aerial parts of Artemisia hispanica and chromatographic separation yielded the eight known sesquiterpene lactones costunolide, artemorin, anhydroverlotorin, tamaulipin A, reynosin, santamarin, matricarin and deacetylmatricarin, the flavone cirsimaritin, zingerone, 1-hydroxy-α-bisabololoxide A acetate and the new germacranolide 2α-hydroxyartemorin.
Sesquiterpenes from Centaurea aspera
2005
Abstract 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.
Synthesis and biological evaluation of cyclic derivatives of combretastatin A-4 containing group 14 elements
2018
Several tricyclic compounds inspired by the structure of combretastatin A-4 and bearing group 14 elements have been synthesized by homocoupling lithiated aryl fragments followed by ring-closing metathesis. These tricyclic compounds and their diolefin precursors were evaluated for their antiproliferative action on the tumor cell lines HT-29, MCF-7, HeLa and A-549 and on the non-tumor cell line HEK-293. In addition, their effects on the cell cycle were also measured. The tricyclic compounds show antiproliferative activity similar to that of combretastatin A-4, even though they are not so active in arresting the cell cycle. However, some diolefin precursors are able to cause accumulation of ce…
Tigliane diterpenes from the latex of Euphorbia obtusifolia with inhibitory activity on the mammalian mitochondrial respiratory chain
2003
Abstract 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±0.3 mM. 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.
Stereoselective synthesis of the naturally occurring 2-pyranone dodoneine
2008
The first total synthesis of the naturally occurring dihydropyranone dodoneine is reported. Asymmetric allylation reactions were used for the stereoselective generation of the two stereogenic centers. The pyranone ring was created by ring-closing metathesis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Influence of structural factors and enzyme type on the reactivity and enantioselectivity of the enzymatic esterification of bicyclic meso dialcohols
1992
The meso dialcohols 1–7, obtained from the Diels-Alder adducts furan/maleic anhydride, furan/dimethyl acetylenedi-carboxylate, and cyclopentadiene/maleic anhydride, were subjected to enzymatic esterification in organic solvents. A mixture of the corresponding chiral monoacetates and the meso diacetates was obtained. It has been found that reaction rate and enantioselectivity markedly depend on substrate structure, temperature, enzyme type, and nature of the solvent. The presence of an oxygen bridge and an exo configuration are the two structural features which lead to the highest enantioselectivity values.
Stereoselective Synthesis of the Antiprotozoal Lactone Passifloricin A and Seven Isomers Thereof
2004
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.
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-enoi…
2003
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]
Terracinolides from Euphorbia terracina
1997
Abstract The aerial parts of Euphorbia terracina yielded five new bishomoditerpene lactones, named terracinolides C-G, which display the novel C 22 17-ethyljatrophane framework.
Sesquiterpene lactones from Artemisia herba-alba
1990
Abstract The aerial parts of Artemisia herba-alba subsp. valentine yielded, in addition to known compounds, a new germacranolide, six new eudesmanolides and ilicic acid methyl ester.
Sesquiterpene lactones and acetylenes from Artemisia reptans
1994
Abstract The aerial parts of Artemisia reptans yielded a new thiophene acetylene, four new guaianolides, a new acyclic sesquiterpene related to davanone and several known compounds.
Stereoselective synthesis of the published structure of feigrisolide A. Structural revision of feigrisolides A and B.
2006
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.
Oplopanone derivatives monoterpene glycosides from Artemisia sieberi
1993
Abstract The aerial parts of Artemisia sieberi yielded three new oplopanone derivatives, three new monoterpene glycosides, a new germacrane alcohol and a monoterpene acid related to nerolidol.
Synthesis of umbellifolide and three natural eudesman-12,8-olides from (-)-artemisin
1987
Abstract The syntheses of the natural 4,5-secoeudesmanolide 1 (umbellifolide) and the eudesmanolides 2, 3 and 4 are described. The starting materials are synthetic eudesmane derivatives, the preparation of which from (-)-artemisin had been previously reported.
ChemInform Abstract: Stereoselective Synthesis of syn-α-Methyl-β-hydroxy Esters.
2000
Abstract Boron enolates of an ethyl ketone structurally related to erythrulose react with achiral aldehydes in a highly stereoselective fashion to yield 1,2- syn /1,3- syn stereoisomers. Oxidative cleavage of the aldol adducts yields enantiopure O -formylated syn -α-methyl-β-hydroxy esters, easily cleaved to the corresponding hydroxyl-free compounds. The aforementioned ketone behaves therefore as a chiral propionate enolate equivalent.
Enzyme-mediated enantioselective acylation of secondary amines in organic solvents
1991
Abstract Porcine pancreatic lipase (PPL) and lipase Amano P catalyze the enantioselective acylation of cyclic 1,2- and 1,3-amino alcohol derivatives in organic solvents. The enatiomeric excesses (ee′s) were shown to depend on the enzyme, reaction time, temperature and type of substrate.
Stereoselective Total Synthesis and Absolute Configuration of the Natural Decanolides (−)-Microcarpalide and (+)-Lethaloxin. Identity of (+)-Lethalox…
2005
[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.
Influence of conformational factors on acid-catalyzed cyclizations of germacranolides: Molecular structure of the cyclization products of gallicin an…
1995
Acid-catalyzed cyclization of the natural germacranolide gallicin (8) yielded, among other products, the 1,4-epoxyeudes-manolide 9, which has a trans-fused decaline system. Under the same conditions the closely related germacranolide shonachalin A (8α-hydroxygallicin) (3) cyclized to the eudesmanolide 4 with a cis fused decaline system. The structures of these cyclization products were secured by means of chemical correlations and X-ray diffraction analyses.
Oxygenated germacranes from Santolina chamaecyparissus
1993
The polar fraction of an extract of Santolina chamaecyparissus ssp. squarrosa yielded six new germacrane derivatives and a novel seco-germacrane lactone. The structures have been derived from spectral data, X-ray diffraction and chemical correlations.
A Synthetic Model for the [4+2] Cycloaddition in the Biosynthesis of the Brevianamides, Paraherquamides, and Related Compounds
2000
Abstract The reactivity of model systems for the proposed [4+2] cycloaddition in the biosynthesis of the brevianamides, paraherquamides, and marcfortines is explored. The model for the intermolecular reaction reveals that the cycloaddition takes place under mild conditions only if activated, very reactive dienophiles are used. When relatively unreactive dienophiles such as cyclopentene and cyclohexene are used, harsh reaction conditions and/or a Lewis acid catalyst are necessary for the reaction. In contrast, the model for the intramolecular reaction demonstrates that the cycloaddition takes place within a few hours at room temperature, even in the absence of a Lewis acid catalyst. Conclusi…
Two isorhamnetin triglycosides from Anthyllis sericea
1989
Abstract A fraction of a methanolic extract of aerial parts of Anthyllis sericea yielded vicenin 2 and the two new compounds isorhamnetin 3- O -(2- O -β-glucopyranosyl-6- O -α-rhamnopyranosyl)-β-galactopyranoside and isorhamnetin 3- O -(2- O -β-glucopyranosyl)-βl-galactopyranoside-7- O -β-glucopyranoside.
Diastereoselective synthesis of enantiomeric tertiary alcohols via nucleophilic additions to protected D- and L-erythrulose derivatives
1992
Abstract The diastereoselectivity of the addition of several organometallic reagents to the carbonyl group of protected D - and L -erythrulose derivatives has been investigated. Tertiary alcohols are stereoselectively formed, the diastereomeric ratio being markedly dependent on the reagent type, solvent and temperature.
Synthesis of (±)-(E)-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid and the corresponding amide (“acacialactam”)
1994
Abstract The total synthesis of the title compounds in racemic form is described. Linalool was used as the starting material and transformed into the target molecules in 6 steps. The synthetic amide displays spectral properties identical to those reported for the natural compound acacialactam, indicating that the structure proposed for the latter compound is not correct.
Sesquiterpene lactones, lignans and aromatic esters from Cheirolophus species
1994
Abstract The aerial parts of five Cheirolophus species yielded three new guaianolides, a new lignan and three new aromatic esters, together with other known compounds of the same type.
Sesquiterpene lactones from Picris echioides
1992
Abstract The aerial parts of Picris echioides yielded the new germacranolide 3β-hydroxybalchanolide and the known guaianolides hieracin I, hieracin II, 8-deoxylactucin, jacquilenin and 11 -epijacquilenin.
A germacrane derivative from Pallenis spinosa
1991
Abstract Extraction of aerial parts of Pallenis spinosa and chromatographic separation have yielded a new germacrane derivative and the known sesquiterpenes shiromool and α-cadinol.
Germacrane derivatives from Santolina chamaecyparissus
1991
Abstract The aerial parts of Santolina chamaecyparissus subsp. squarrosa yieleded five new germacrane derivatives and a known eudesmane dialcohol.
Stereoselective Synthesis and Structural Correction of the Naturally Occurring Lactone Stagonolide G
2010
A convergent synthesis of the structure proposed for the naturally occurring lactone stagonolide G is described. All three stereocenters were created with the aid of asymmetric Brown allylations. The lactone ring was built by means of a ring-closing metathesis (RCM). The synthetic and the natural compound differed in their spectral properties. A new structure is now proposed for stagonolide G and demonstrated by means of a chemical transformation.
Total synthesis of (−)-mintlactone
1991
Abstract The first total, stereodirected synthesis of (—)-mintlactone is described. A stereoselective, radical-mediated ring closure was the key step in the synthesis.
Caryophyllene derivatives from Pulicaria dysenterica
1992
Abstract A reinvestigation of the aerial parts of Pulicaria dysenterica has allowed the isolation of six new caryophyllene derivatives and 12 known ones. 13 C NMR data of all these derivatives are reported.
Phenolic and acetylenic metabolites from Artemisia assoana
1987
Abstract Nine flavones, three coumarins, two flavone glycosides, p-hydroxyacetophenone and methyl caffeate have been isolated from the aerial parts of Artemisia assoana. Six diacetylenic spiroketal enol-ethers, a mixture of n-alkyl p-coumarates and a new phenylpropanoid metabolite, sinapyl alcohol diisovalerate, have been isolated from root extracts of the same plant. 1H and 13C NMR spectra of some of these compounds are given and taxonomic aspects are discussed.
Boron aldol additions with erythrulose derivatives: dependence of stereoselectivity on the type of protecting group
1999
Abstract Boron aldol additions of 1- O -silylated 3,4-di- O -benzyl- and 3,4-di- O -benzoyl- l -erythrulose and achiral aldehydes using dicyclohexylboron chloride have been investigated. The dibenzyl derivative gave syn/syn stereoisomers with high stereoselectivity, whereas the dibenzoyl derivative gave syn/anti stereoisomers. It is believed that, while the dibenzoyl erythrulose gives rise to the E enolate in the presence of dicyclohexylboron chloride, as usually observed with this reagent, only the Z enolate is formed in the case of the dibenzyl derivative.
Absolute Configurations of Three Naturally Occurring Acetylenic Spiroacetal Enol Ethers
1993
The absolute configurations of three 6,7-oxygenated acetylenic spiroacetal enol ethers were determined by using the kinetic method of Horeau. The results were confirmed by the circular dichroism of the compounds in correlation with the corresponding 6,7-epoxide.
Sesquiterpene lactones from Artemisia lucentica
1997
Abstract The aerial parts of Artemisia lucentica yielded, in addition to several known compounds, a bicyclic monoterpene ketone, two germacranolides, an eudesmanolide, a 10- epi neudesmanolide, a 2-norelemanolide and three bisabolene derivatives. The stereochemistry of a germacranolide, described as 2α-hydroxyartemorin in a previous investigation of the species, has now been corrected and the compound has been renamed lucentolide.
syn-1,6-imino-8,13-oxido[14]annulene
1990
Abstract syn -1,6-Imino-8,13-oxido[14]annulene (1) , an aromatic annulene featuring closely spaced NH and O-bridges, has been synthesized. Contrary to expectation, NH ⋯ O hydrogen bonding in I does not profit from the proximity of the functionalities noticeably.
Jatrophane and tigliane diterpenes from the latex of Euphorbia obtusifolia
1999
The latex of Euphorbia obtusifolia var. obtusifolia yielded twelve new diterpene polyesters. Seven of them displayed the jatrophane framework and five were 4-deoxyphorbol esters. A further isolated tigliane diterpene, a derivative of 4-epi-4-deoxyphorbol, was most likely an artifact of the isolation procedure. All structures were established with the aid of spectroscopic methods.
Arylpyridines, arylpyrimidines and related compounds as potential modulator agents of the VEGF, hTERT and c-Myc oncogenes.
2019
Twenty-four derivatives structurally related to honokiol have been synthesized and biologically evaluated. IC50 values were determined towards the HT-29, MCF-7 and HEK-293 cell lines. Some of these derivatives exhibited comparable or lower IC50 values than honokiol towards the HT-29 and MCF-7 cell lines or else higher selectivity indexes than the natural product. Twelve selected derivatives were evaluated for their ability to inhibit the expression of the VEGFA, hTERT and c-Myc genes and also to inhibit the production of total c-Myc protein and the secretion of the VEGF protein. One of the most promising compounds, 3-(2,4-dimethoxyphenyl)pyridine, may be a good candidate for further studies…
ChemInform Abstract: A Stereoselective Synthesis of (+)-Malyngolide via a Ring-Closing Olefin Metathesis.
2000
Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.
Sesquiterpene lactones from Artemisia species
1993
Abstract The aerial parts of Artemisia spicigera yielded two new eudesmanolides as well as three known ones. The aerial parts of Artemisia verlotiorum yielded four known germacranolides and two known eudesmanolides.
Stereoselective synthesis and determination of the cytotoxic properties of spicigerolide and three of its stereoisomers.
2003
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.
Stereoselective synthesis of syn-α-methyl-β-hydroxy esters
2000
Abstract Boron enolates of an ethyl ketone structurally related to erythrulose react with achiral aldehydes in a highly stereoselective fashion to yield 1,2- syn /1,3- syn stereoisomers. Oxidative cleavage of the aldol adducts yields enantiopure O -formylated syn -α-methyl-β-hydroxy esters, easily cleaved to the corresponding hydroxyl-free compounds. The aforementioned ketone behaves therefore as a chiral propionate enolate equivalent.
Stereoselective synthesis of the cytotoxic 14-membered macrolide aspergillide A.
2010
A stereoselective synthesis of the cytotoxic 14-membered macrolide aspergillide A has been performed. The preparation of a cis-2,6-disubstituted tetrahydropyran ring via stereoselective reduction of an intermediate cyclic hemiacetal was one key feature of the synthesis. The macrocyclic lactone ring was created by means of a ring-closing metathesis (RCM), whereby the new C=C bond displayed exclusively the undesired Z configuration. Conversion to the required E configuration was achieved via photochemical isomerization.
Revision of the structure of torrentin
1989
Abstract The structure of the eudesmanolide torrentin from Artemisia herba-alba subs valentine has been revised on the basis of high-field 1 H NMR spectroscopy and chemical correlations.
Bisabolene derivatives and sesquiterpene lactones from Cousinia species
1993
Abstract The aerial parts of three species of the genus Cousinia have been investigated. All three species yielded sesquiterpene lactones, mainly guaianolides. In addition, one of the species yielded oxygenated bisabolene derivatives.
A sesquiterpene ester from Lactuca serriola
1992
Abstract The aerial parts of Lactuca serriola yielded a new guaiane ester together with five known guaianolides.
Stereoselective synthesis of the naturally occurring styryllactones (+)-goniofufurone and (+)-cardiobutanolide.
2004
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.
Stereoselective anti aldol reactions of erythrulose derivatives. Functionalized chiral d3 and d4 synthons.
2004
An improved procedure for the synthesis of anti aldols from protected erythrulose derivatives is reported. The preparation of functionalized d3 and d4 synthons with various stereochemical arrays by means of this methodology is described and subsequently applied to a stereoselective formal synthesis of the natural metabolite goniothalesdiol.
A novel germacranolide-aminoacid adduct dimer from centaurea aspera
1991
Abstract The novel germacronolide-valine adduct dimer 1 has been isolated from aerial parts of Centaurea aspera var. aspera . Its structure has been determined by spectroscopic methods.
ChemInform Abstract: Boron Aldol Additions with Erythrulose Derivatives: Dependence of Stereoselectivity on the Type of Protecting Group.
2010
Abstract Boron aldol additions of 1- O -silylated 3,4-di- O -benzyl- and 3,4-di- O -benzoyl- l -erythrulose and achiral aldehydes using dicyclohexylboron chloride have been investigated. The dibenzyl derivative gave syn/syn stereoisomers with high stereoselectivity, whereas the dibenzoyl derivative gave syn/anti stereoisomers. It is believed that, while the dibenzoyl erythrulose gives rise to the E enolate in the presence of dicyclohexylboron chloride, as usually observed with this reagent, only the Z enolate is formed in the case of the dibenzyl derivative.
Germacranolides and a monoterpene cyclic peroxide from Artemisia fragrans
1998
Abstract The aerial parts of Artemisia fragrans collected in Armenia yielded a new cyclic monoterpene peroxide with the irregular santolinyl framework, together with several known germacranolides. Comparison with previously published chemical results suggests these may actually have been performed on a different, although closely related species.
One electron transfer chain decomposition of trifluoroacetone diperoxide: The first 1,2,4,5-tetroxane with O-transfer capability
1992
Abstract Reaction of 1,1,1-trifluoropropanone (trifluoroacetone) ( 1a ) with 30% hydrogen peroxide in the presence of conc. sulfuric acid afforded in good yield 3,6-bis(trifluoromethyl)-3,6-dimethyl-1,2,4,5-tetroxane or trifluoroacetone diperoxide ( 2a ). Peroxide 2a is quantitatively converted into trifluoroacetone ( 1a ) and dioxygen by a catalytic amount of tetrabutylammonium iodide through a reductive electron transfer chain reaction carried out by the superoxide ion. Trifluoroacetone diperoxide ( 2a ) is capable of O-atom transfer to alkenes and sulfides.
Stereoselective Synthesis of the Cytotoxic Macrolide FD-891
2006
[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.
Synthesis and Biological Evaluation of α-Tubulin-Binding Pironetin Analogues with Enhanced Lipophilicity
2013
Financial support has been granted to M. C. by the Spanish Ministry of Education and Science (project numbers CTQ2008-02800 and CTQ2011-27560), by the Conselleria d'Empresa, Universitat i Ciencia de la Generalitat Valenciana (ACOMP09/113) and by the BANCAJA-UJI Foundation (P1-1B2002-06, P1-1B-2008-14 and PI-1B2011-37). The biological work has been supported in part by grants from the Spanish Ministry of Education and Science (grant number BIO2010-16351) and from the Comunidad de Madrid (grant number S2010/BMD-2457 BIPEDD2-CM), both to J. F. D. We further thank the Matadero Municipal Vicente de Lucas in Segovia for providing the calf brains, which were the source of tubulin.
Double diastereoselection in aldol reactions mediated by dicyclohexylchloroborane between L-erythrulose derivatives and chiral aldehydes. The Felkin-…
2003
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.
Highly diastereoselective additions of organometallic reagents to 1-O-silylated 3,4-Di-O-benzyl-L-erythrulose derivatives
1993
Abstract The diastereoselectivity of the addition of several organometallic reagents to the carbonyl group of the title compounds has been investigated. Some organomagnesium reagents display high diastereoselectivities (90–99%) and the major products are those predicted by the α-chelation model.
Total synthesis of the monoterpenes (−)-mintlactone and (+)-isomintlactone
1992
Abstract The first total stereodirected synthesis of the monoterpenes (−)-mintlactone and (+)-isomintlactone from the same chiral starting product is described. A stereoselective, radical-mediated ring closure was the key step in both syntheses.
Sesquiterpene lactones and lignans from Centaurea species
1992
Abstract The aerial parts of Centaurea calcitrapa yielded cnicin, cnicin 4′-acetate, melitensin, a related elemanolide, the two new germacranolides 11α,13- and 11β,13-dihydrosalonitenolide, and the lignans arctigenin, pinoresinol and 7′( S )-hydroxyarctigenin. The latter compound is described for the first time as a natural product. The aerial parts of Centaurea pabotii yielded 11,13-dihydrodeacylcynaropicrin, aguerin A and a new guaianolide related to cynaropicrin.
A stereoselective synthesis of (+)-malyngolide via a ring-closing olefin metathesis
2000
Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.
Stereoselective Syntheses of Naturally Occurring 5,6-Dihydropyran-2-ones
2007
The published syntheses of naturally occurring 5,6-dihydropyran-2-ones are reviewed. Figure options Download full-size image Download as PowerPoint slide
Ingenane and lathyrane diterpenes from the latex of Euphorbia canariensis
1997
The latex of Euphorbia canariensis yielded, in addition to five known ingenol esters, the ingenane derivatives ingenol 3-angelate 5,20-diacetate and 5-deoxyingenol 3-angelate 20-acetate, and the lathyrane derivatives 2,3-diepiingol 7,12-diacetate 8-benzoate, 2,3-diepiingol 7,12-diacetate 8-isobutyrate and 2-epiingol 3,7,12-triacetate 8-benzoate. The structures were established with the aid of spectroscopic methods, mainly NMR, and molecular mechanics calculations. They were also supported by the results of some chemical transformations.
Synthesis of Combretastatin A-4 and 3′-Aminocombretastatin A-4 derivatives with Aminoacid Containing Pendants and Study of their Interaction with Tub…
2020
Natural product combretastatin A-4 (CA-4) and its nitrogenated analogue 3&prime
New oxygenated eudesmanolides from artemisia herba-alba
1990
Abstract The aerial parts of Artemisia herba-alba Asso subsp.valentina Lam. (Asteraceae) yielded the new eudesmanolides 1-11 and the new sesquiterpene-monoterpene adducts 12-13. The absolute configuration of compound 6 was confirmed with the aid of X-ray diffraction analysis. Some aspects of the thermal and photochemical reactivity of 2,4-cyclohexadienones are discussed.
Oxygenated nerolidol esters and eudesmane acids fromInula viscosa
1991
Abstract The aerial parts of Inula viscosa yielded three new esters of 9-hydroxynerolidol and two new eudesmane acids, along with several known compounds.
Sesquiterpene lactones fromArtemisia barrelieri
1991
Abstract Extraction of aerial parts of Artemisia barrelieri and chromatographic separation yielded a new germacranolide, two new monocyclic sesquiterpenes and a novel germacranolide dimer, together with several known compounds.
Stereoselective 1,3-Dipolar Cycloadditions of a Chiral Nitrone Derived from Erythrulose. An Experimental and DFT Theoretical Study
2000
We have investigated several 1,3-dipolar cycloadditions of a chiral nitrone prepared from L-erythrulose. While cycloadditions to carbon-carbon multiple bonds of dipolarophiles such as ethyl acrylate, ethyl propiolate, or dimethyl acetylenedicarboxylate were poorly stereoselective, reaction with acrylonitrile provided predominantly one diastereomeric adduct. Furthermore, the regioselectivity exhibited by the two structurally similar dipolarophiles ethyl acrylate and ethyl propiolate was found to be opposite. The molecular mechanisms of these cycloadditions have thus been investigated by means of density functional theory (DFT) methods with the B3LYP functional and the 6-31G and 6-31+G basis …
Germacrane esters from roots of Ligularia persica
1991
Abstract Extraction of roots of Ligularia persica and chromatographic separation yielded one new derivative of tovarol, four new derivatives of shiromodiol, α- and β-eudesmol, bakkenolide A and four known eremophilane derivatives.
Chlorodicyclohexylborane-mediated aldol additions of alpha,alpha'-dioxygenated ketones.
2001
Boron aldol additions of variously O-protected alpha,alpha'-dioxygenated ketones using dicyclohexylboron chloride and a tertiary amine have been investigated. The stereoselectivity of the process was dependent on the protecting group on the alpha-oxygen atoms. Notably, ketones with bulky silyloxy groups gave syn aldols, most likely via Z enolates. This rules out the participation of chelates during the enolization process, at least in the presence of such sterically crowded protecting groups. An alternative explanation is offered.
Synthesis of Protected Enantiopure Erythrulose Derivatives
1996
D- and l-Erythrulose derivatives 2–6 bearing protective O-silyl and O-benzyl groups in various positions were synthesized in enantiopure form from l-ascorbic acid, D-isoascorbic acid, and D-glucose.
Design and synthesis of pironetin analogue/colchicine hybrids and study of their cytotoxic activity and mechanisms of interaction with tubulin
2014
We here report the synthesis of a series of 12 hybrid molecules composed of a colchicine moiety and a pironetin analogue fragment. The two fragments are connected through an ester-amide spacer of variable length. The cytotoxic activities of these compounds and their interactions with tubulin have been investigated. Relations between the structure and activity are discussed. Since the spacer is not long enough to permit a simultaneous binding of the hybrid molecules to the colchicine and pironetin sites on tubulin, a further feature investigated was whether these molecules would interact with the latter through the pironetin end (irreversible covalent binding) or through the colchicine end (…
Stereoselective Synthesis of the Glycosidase Inhibitor Australine through a One-Pot, Double-Cyclization Strategy
2006
[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.
Synthesis of N-acyl Derivatives of Aminocombretastatin A-4 and Study of their Interaction with Tubulin and Downregulation of c-Myc.
2021
11 p.-9 fig.-4 tab.