Gabor Lukacs

Solvent-Free Synthesis of Decyl D-Glycopyranosides Under Focused Microwave Irradiation

Abstract A three step microwave assisted solvent-free synthesis of decyl D-glucopyranoside with 1-decanol was established for D-glucose and extended to D-galactose, D-mannose and N-troc-D-glucosamine with 70% average overall yield for the three steps (peracetylation, glycosylation and saponification). Rate enhancements and reduction of the reaction time were observed for the two last steps carried out under microwave irradiation when compared to conventional heating in the same conditions.

Synthesis of α-azido aldehydes. Stereoselective formal access to the immunosuppressant myriocin

Abstract Stereoselective preparation of an acyclic α-azido aldehyde permitted access in a few steps to a key intermediate in a formal synthesis of myriocin.

Synthesis of two enantiomeric tetrasubstituted cyclohexanones from 6-deoxyhex-5-enopyranoside derivatives

Abstract The conversion of various 6-deoxyhex-5-enopyranoside derivatives in the presence of a catalytic amount of mercury(II) sulfate into chiral cyclohexanones has been studied. Under the experimental conditions used, the stereochemistry at position 5 of the tetrasubstituted cyclohexanones appears to depend on the conformation of the starting carbohydrate derivatives which was indicated by the 13C-n.m.r. data. Reaction of methyl 4-O-benzoyl-2,3-di-O-methyl-β- l -arabino- and -α- d -arabino-hex-5-enopyranoside furnished the enantiomeric 2-benzoyloxy-5-hydroxy-3,4-dimethoxycyclohexanones 19 and 21, respectively.

Cycloaddition Reactions of Carbohydrate Derivatives. Part III. A New Route to Swainsonine Analogs.

Abstract Swainsonine analogs 10 and 12 have been synthesized from D- and L-arabinose, respectively, using cyclocondensation of azomethines with Danishefskys diene followed by stereoselective carbonyl and double bond reduction of the resulting pyridones, chain shortening and ring closure by reductive amination.

Alkaloids of Alstonia lanceolifera

Abstract Four new indole alkaloids, 10-methoxydeplancheine, 10,11-dimethoxy-1-methyl-deacetyl picraline benzoate, 10,11-dimethoxy-1-methyl-deacetyl picraline 3′,4′,5′-trimethoxybenzoate and 10,11-dimethoxy-1-methyl-deacetyl picraline were isolated from the leaves of Alstonia lanceolifera .

Total structure of the polythiazole-containing antibiotic micrococcin P. A 13C nuclear magnetic resonance study

The structure of the antibiotic micrococcin P has been determined by 13C n.m.r. spectroscopy.

10-Epijunenol, a new cis-eudesmane sesquiterpenoid

Abstract An unusual cis-eudesmane sesquiterpene alcohol has been isolated from galbanum resin. Some comments about the spectral properties of cis-decalins with angular methyl groups are made. A new synthesis of the selinane system is described.

Cycloaddition reactions of carbohydrate derivatives. Part VI. Quinolizidine analogs of castanospermine

Abstract Octahydroquinolizine-1,2,3,8-tetraols 12, 16 and 23, analogs of castanospermine, were synthesized from D-glucose, L-arabinose and D-mannose, respectively, using hetero-Diels-Alder reactions of sugar-derived azomethines as the key step.

Efficient routes to pyranosidic homologated conjugated enals and dienes from monosaccharides

Abstract Three new processes for the obtention of pyranosidic dienes type B, and D and homologated conjugated enals A, have been designed in the context of the preparation of useful chiral building blocks from monosaccharides. Addition of vinylmagnesium bromide onto ulose 1 , followed by acetal ring opening; benzoate protection at C-4 and C-6; and dehydration of the tertiary hydroxyl group, mediated by thionyl chloride, reveals to be a straigthforward route to diene 11 . Analogous dehydration on conformationally rigid 2 was not regioselective and afforded isomeric dienes 3 and 6 in a 1:1 ratio. Addition of 2-lithio-1,3 dithiane onto locked 2,3-anhydropyranoses 21 and 22 followed by unravelling of the S,S-acetal moiety led efficiently to homologated α-enals 26 , 27 , 31 , and 30 and hence to dienes 34 , 14 , 20 and 13 through Wittig methylenation. Finally α-alkoxyvinyl ethers, prepared either by Wittig-Horner reaction of α-alkoxy-uloses, or by hetero Diels-Alder reaction of conjugated-enals, afforded in good to excellent yields pyranosidic α-enals 37 , 42 , 43 , 44 , 50 and 51 on treatment with pyridinium hydrochloride in pyridine or a mixture acetic acid-water (4:1).

Stereospecific access to branched-chain carbohydrate synthons.

Abstract Appropriate precursors for the synthesis of D-vancosamine and L-evernitrose have been stereospecifically obtained from methyl 4,6-O-benzylidene-2-deoxy-α- and β-D-threo-hexopyranosid-3-ulose.