Stefan L. Spassov

Nuclear magnetic resonance spectra, configuration and conformation of diastereomers: 3-Substituted 2,3-diphenylpropanoic acids and their methyl esters

Abstract The NMR spectra of the erythro and threo forms of compounds of the type PhCHAXCHB(Ph) COOR, where X = OH, OAc, NH2, NHMe, NHPh, NHCONH2, NHCONHAc, and R = H or Me have been investigated in CDCl3 and DMSO-d6 solutions at normal and in some cases also at higher temperature. The values of the vicinal coupling constant JAB are used to study the conformational equilibrium of the erythro and threo forms and its dependence on the solvent and temperature. It is shown that the chemical-shift difference and the shape of the signals of some proton groups as R = Me and Ph are criteria permitting an unequivocal assignment of relative configuration of diastereomers of such type as well as their quantitative determination in complex mixtures.

Neo-clerodane diterpenoids from Ajuga chamaepitys.

Abstract Two new neo -clerodane diterpenoids, ajugachin A and ajugachin B, as well as the previously known ajugapitin and 14,15-dihydroajugapitin have been isolated from Ajuga chamaepitys . The structure and configuration of the new compounds have been elucidated on the basis of spectral studies, in particular 1D and 2D 1 H and 13 C NMR spectra.

Nuclear magnetic resonance spectra, configuration and conformation of diastereomers—II : Ethyl esters of 3-substituted 2,3-diphenylpropanoic acids: Magnetic nonequivalence induced by two asymmetric centres

Abstract The NMR spectra of the erythro and threo forms of the esters PhCH a XCH b (Ph)COOC 2 H 5 , where X = OH, NH 2 , NHPh, and NHCONH 2 have been investigated in CDCl 3 , DMSO-d 6 , benzene and pyridine solutions. Study of the conformational distribution based on the values of the vicinal coupling constants J ab showed that the conformer with antiperiplanar methine protons is the favored one for both diastereomers. Some chemical-shift criteria permitting the assignment of relative configuration of diastereomeric compounds of such type were established. It was shown by use of suitable model compounds that the magnetic nonequivalence of the methylene protons observed in some solvents might be attributed not to either of the asymmetric centres taken alone, but rather to the dissymmetry of the molecule as a whole.

Iridoid glycosides from Linaria species

Abstract The iridoid composition of four Liniria species has been investigated. Two new iridoids along with known compounds were isolated and identified. The new iridoid glucoside, 7,8-epi-antirrinoside, found in L. dalmatica, is the first iridoid glucoside with an α-orientation of the 7,8-epoxide ring, while 6β-hydroxyantirride, found in L. genistifolia and L. peloponnesiaca, appears as a second representative of the rare antirride iridoid type. Antirride was found for the first time in L. simplex. Structure elucidations were carried out mainly by spectral methods and molecular mechanics calculations. Chemosystematic relationships are also discussed.

Thiophene ring formation during the interaction of alkylsulfenyl chlorides with esters of 3-methyl-1,2,4-pentatrienephosphonic acid

Abstract Dialkyl esters of 3-methyl-1,2,4-pentatrienephosphonic acid react with alkylsulfenyl chlorides to produce dialkyl esters of 2-thienylphosphonic acid.

Cyclocondensations of homophthalic anhydrides with 1-aza-1,3-dienes

Abstract α,β-Unsaturated aldimines (1-aza-1,3-butadienes) 2, 4 and 7a-d react with homophthalic anhydrides 1a,b to give 3,4-dihydro-1(2H)-naphthalenone-4-carboxylic acids 3, 5, 8a-d (R2 = H) as main products. Homophthalic anhydride 1a and cinnamaldimine 7d gave rise to the diastereoisomeric naphthalenones 8d (R2 = H), along with the 3,4-dihydro-1(2H)-isoquinolinone-4-carboxylic acids 10 (R2 = H), and 3,4-dihydro-1(2H)-pyridinone 11 (R2 = H) as products of 3,4-, 1,2- and 1,4-addition to the 1-aza-1,3-butadiene, respectively. The effect of the reaction conditions on the ratio of adducts, produced by 1a and 7d, was studied. The structure and relative configurations of 3, 5, 8a-d, 10 and 11 were determined by NMR spectroscopy. In the case of cis-naphthalenone 8c and dihydropyridinone 11, the structure was confirmed by X-ray crystal structure analysis.

Scutorientalin D, a neo-clerodane diterpenoid from Scutellaria orientalis subsp. pinnatifida

Abstract A new neo-clerodane diterpenoid, scutorientalin D, was isolated from the acetone extract of the aerial parts of Scutellaria orientalis subsp. pinnatifida. The structure and configuration of this compound was established by spectroscopic and molecular mechanics methods as (13S)-11β, 19-diacetoxy-4α,18;8β,13-diepoxy-6α-isobutyroxy-neo-clerodan-15,16-olide.

Teulamifin B, a neo-clerodane diterpenoid from Teucrium lamiifolium and T. Polium

Abstract From the aerial parts of Teucrium lamiifolium and T. polium , a neo-clerodane diterpenoid, teulamifin B has been isolated, besides the previously known diterpenoids 19-deacetylteuscorodol and teucroxide. The structure of teulamifin B[15,16-epoxy-6β,12 S ,18-trihydroxy-neo-cleroda-3,13(16),14-trien20,19-olide] was established by chemical and spectroscopic means and by correlation with 19-deacetylteuscorodol.

Reactions of α-chloroimines with homophthalic anhydrides. Synthesis and molecular structure of 3,3a-dihydrofuro[3,4-c] isoquinoline-1,5(4h,9bh)-diones, furo[3′, 4′:9,9α]-8,9,16,16a-tetrahydro-1h,3h,11h-dibenzo[a,g]quinolizine-1,11-diones and related compounds

Abstract The reaction of α-chloroimines 1 - 3 , resp. 11 with homophthalic anhydrides 4 leads to the formation of the isoguinoline ring system incorporated in furo[3,4-c]isoquinolinediones 8 - 10 , resp. 13a-(chloromethyl)-8H- dibenzo[a,g]-quinolizine-8-one-13-carboxylic acids 12 . The latter compounds were converted into furo[3′ 4′:9,9a]dibenzoquinolizinediones 13 under basic conditions. NMR studies provided information concerning the relative configuration and the solution conformation of the various heterocycles obtained. The molecular structure of 8b and 12b was determined by X-ray analysis.

Conformational studies of some 2-phenylpropyl derivatives by NMR spectroscopy and use of lanthanide shift reagents

Abstract The conformational distribution of CH 3 CH(Ph)CH 2 X (X = OH, OCH 3 , NH 2 Cl) has been studied by NMR and IR spectroscopy. The results are interpreted in favour of the conformers with methoxy- or chloro-groups anti to the phenyl group, but the amino group anti to the methyl group. For the alcohol both forms are about equally populated. It is suggested that intra-molecular hydrogen bonding might be affecting the conformational equilibria when X = OH, NH 2 .