[The cis-trans isomerization of aromatic heptaenes catalyzed by sulfur and phosphorus compounds]. / Tsis-trans-izomerizatsiia aromaticheskikh geptaenov, kataliziruemaia soedineniiami sery i fosfora.

It was shown that sulfur and phosphorus compounds (sodium thiosulfate, sodium tripolyphosphate, sodium hexametaphosphate, monosodium phosphate) catalyze cis-trans isomerization of aromatic heptaens. Preparative method of levorin isomerezation at the presence of sodium thiosulfate was elaborated. The isolated product was a fully trans-isomer.

[A laboratory method for sensitized isomerization of polyene macrolides]. / Laboratornyi metod sensibilizirovannoi izomerizatsii polienovykh makrolidov.

The study was aimed at the development of a laboratory procedure for isomerization of polyene macrolides in the presence of sensitizers. The reaction was performed with exposure of levorin solutions to the xenon lamp irradiation in the presence of rose bengal B as a sensitizers. It was shown that levoristatin contain in the levorin sample was not degraded under the experimental conditions. The use of a redetermined variant of the Vierordt's methods made it possible to offer a design formula for the estimation of the isolevorin content in solutions in the presence of levorin.

[Dye-sensitized photoisomerization of polyenic macrolide antibiotics]. / Sensibilizirovannaia krasiteliami fotoizomerizatsiia polienovykh makrolidnykh antibiotikov.

Photoisomerization of levorin A2, a polyenic macrolide, sensitized by various dyes such as thiazines, acridines, xanthenes and phthalocyanines was studied. The use of the dyes made it possible to shift the isomerization process to the visible spectrum region and to increase the quantum yield to 1. The conditions of the triplet-triplet transfer of the sensitized reaction energy were investigated. By its physio-chemical and biological properties the levorin A2 isomer was identical to the levorin A2 isomer resulting from the direct action on the heptaene chromophore. The dye efficiency was demonstrated in regard to other heptaene antibiotics such as trichomycin and candicidin.

[Spectrophotometric research on the photochemical isomerization of the polyene macrolide antibiotic levorin A2]. / Spektrofotometricheskoe issledovanie fotokhimicheskoi izomerizatsii polienovogo makrolidnogo antibiotika levorin A2.

Photochemical (cis-trans) isomerization of levorin A2 under the effect of light at wave lengths of 313 and 365 nm (excitation of the polyenic system and p-aminobenzoylene respectively) was studied. In case of the polyenic system excitation the reaction was reversible and the process quantum yield was extremely low while the use of light at the wave length of 313 nm as photochemical activator resulted in increasing the quantum yield by two orders. In this case triplet-triplet transfer of energy took place. A calculation procedure is recommended for quantitative determination of the quantum yield of levorin isomerization including direct and reverse reactions. The procedure may be used in study of other objects with similar mechanisms of phototransformation.

[Isomerization of levorin. The structure of isolevorin A2]. / Izomerizatsiia levorina. Struktura izolevorina A2.

The products of retroaldol splitting and azonolysis of isolevorin A2 resulting from UV irradiation of levorin A2 solutions were studied in comparison with the products of the same chemical transformations of the initial levorin A2. The findings enabled to classify isolevorin A2 as a transheptaen. Investigation of the products of retroaldol splitting of isolevorin resulting from chemical isomerization suggested that along with cys- and trans-conversions during chemical isomerization there took place chloroform transference with formation of a branched polyen. NMR spectroscopy revealed 2 free carbonyls in the isolevorin A2 molecule. The other 2 formed the hemiketal rings.

[Optical rotatory dispersion of levorin and isolevorin]. / Dispersiia opticheskogo vrashcheniia levorina i izolevorina

Optical rotation dispersion of levorin A2 and isolevorin A2, macrocyclic heptaen antibiotics in the region of 260--320 nm due to the presence of ketogroups in the molecules of these antibiotics was studied. On the basis of the study of the optical rotation dispersion, diffusion properties and molecular models of the antibiotics it was supposed that levorin and isolevorin differed in the space configuration of the macrocycli lactone ring.

[Optical rotary dispersion of some heptaene antibiotics]. / Dispersiia opticheskogo vrashcheniia nekotorykh geptaenovykh antibiotikov

Experimental differences in the curves of the optic rotation dispersion (ORD) of cystrans-heptaenic antibiotics were found. The ORD curves of amphotericin B, mycoheptin, levorin components and isolevorin A2, components of criptomycin and candidin were registered. The curves of the ORD which were smooth had been prepared in dimethylsulphoxide in the spectral range at 450 to 600 nm. In the spectral range at 300 to 420 nm the ORD curves appeared to be anomal with a complex Kotton effect, they were prepared in methyl alcohol. The Kotton effect was probably due to asymmetry of the electron membranes of polyenic chromophore induced by the other part of the polyen molecule. This was evident from the fact that the curve of the Kotton effect was situated in the same spectral range as the absorption bond of the polyenic chromophore. The oscillating structure in the absorption spectrum and the curve of the complex Kotton effect were analogous.