Cs. Szantay

Synthesis of corynantheidine alkaloids—III : The stereoselective total synthesis of (±)-dihydrocorynantheine☆

Abstract Starting from the normal cyano-acetate derivative 3b, obtained from the allo stereoisomer 3a via an unusual epimerization,1 the stereoselective totalsynthesis of (±)-dihydrocorynantheine (1a) was accomplished.

Synthesis, anti-GABA activity and preferred conformation of bicuculline and norbicuculline enantiomers.

Synthesis of erythro-(±)-[1SR,9RS]-norbicuculline and threo-(±)-[1SR,9SR]-noradlumidine from piperonal was performed using Bischler-Napieralski cyclization as a key step. Resolution gave rise to (+)-[1S,9R]-norbicuculline ([1S,9R] norBIC) and (-)-[1R,9S]-norbicuculline ([1R,9S] norBIC) in >99.5% enantiomeric purity. Bicuculline enantiomers were readily obtained by methylation of the latter products. [1S,9R]BIC was about 70 times more potent than [1R,9S] BIC as an inhbitor of GABA(A) receptor binding and was about 100 and 900 times more potent than [1S,9R] norBIC at pH 7.1 and 5.0 respectively. Similarly, [1S,9R] norBIC was much less potent than [1S,9R] BIC as an inhibitor of GABA-specific (36)Cl(-) ion flux. The observed increase of about two orders of magnitude in the in vitro biological activity caused by N2-CH(3) substitution in [1S,9R] norBIC was attributed to different conformations for erythro- and nor-erythro-bicucullines indicated by (1)H nuclear Overhauser enhancements of [1S,9R] BIC and [1S,9R] norBIC.

Synthesis of corynantheidine alkaloids—II : An unusual epimerization of indolo[2,3-a]- and benzo[a]quinolizidine derivatives☆

Abstract 2,3- cis -Substituted quinolizidine-enamines can be epimerized to the corresponding trans compounds, if suitable substituents are attached to the CH group linked to C atom No. 2. This observation allows the transformation of indolo[2,3-a]- and benzo[a]quinolizidines of allo configuration into their normal stereoisomers. Starting from optically active compounds, it has been established on the basis of their CD curves that the epimerization proceeds at C(2).

Rearrangement of Allyl Aryl Ethers I. Reaction of hydroquinone with conjugated Dien-ols and Trien-ol

Thermal rearrangement of ethers 3 generated in situ from hydroquinone 1 and conjugated polyen-ols 2 afforded 2,3-dihydrobenzofuranols 5, 8 and 10 with 1,3- and/or 3,5-shifts followed by acid-catalyzed intramolecular cyclization.

INVESTIGATION ON THE CHEMISTRY OF BERBANS. VII. SYNTHESIS OF 10,11‐DIMETHOXY(DEPYRROLO)RAUNESCINE STEREOISOMERS

Abstract Acyloxy-ketone rearrangement, proceeding by the action of base, has been observed in the case of ketone 2 . By the reduction of ketones 2 and 3 with sodium boron hydride, new 10, 11-dimethoxy(depyrrolo)raunescine stereoisomers ( 5a–7a ) have been prepared. Previously known alcohols with alloberban skeleton ( 12,13 ) have been similarly converted into tetracyclic raunescine stereoisomers ( 8a,9 ) by the oxido-reductive method. The stereochemistry of these compounds has been investigated by physical ( 1 H NMR, IR) and by chemical methods.

The structure investigation of a new product formed in the course of nitration of apovincaminic acid ethyl ester by NMR methods

Abstract A new 2,7-dihydro-indole derivative formed during the nitration of apovincaminic acid ethyl ester (Cavinton®), has been studied by 1H and 13C NMR spectroscopy. Homo- and heteronuclear NOE (nuclear Overhauser effect) difference measurements, together with homo- and hetero-shift correlation experiments allowed the complete assignment of the NMR spectra, and the elucidation of the constitution and stereochemistry of the molecule.

Structural investigation of a new heterocyclic ring system: NMR and X-ray studies

Abstract The reaction of enamines 4a, b with acrylonitrile gave rise to compounds 6a, b in addition to four ( 7a–10a and 7b–10b ) stereoisomeric derivatives of a new heterocyclic ring system, the structures of which were thoroughly investigated by different spectroscopic methods, in particular by C NMR. Molecular structures of 7a–10a were substantiated by single crystal X-ray diffraction. Crystal data were collected on a CAD-4 diffractometer using monochromatic CuKα radiation (λ = 1.541 80 A) and the model structures determined by direct methods were refined on F 2 values. The conformations of the four diastereomeric molecules are rather similar. The epimerization at C(12) has only a slight effect on the bond angles around the bridge head atom, while the exchange of the -C 2 H 5 and -C 2 H 4 CN functions has practically no impact on the bond lengths, bond angles and torsion angles around C(1). The excellent internal consistency of the molecular geometry permitted characterization of the bond lengths of C(sp 3 )-X (X  C(sp 3 ), C(aryl), C(sp), etc.) types.