A. L. Mikhal'chuk

Specific Fluorescence Properties and Picosecond Transient Absorption of 8-Azasteroids

The specific fluorescence properties as well as picosecond transient absorption features have been studied for two 8-azasteroids. It is shown that at various excitation wavelengths the essentially different final excited electronic states are realized. Because of the multicenter character of 8-azasteroids the spectroscopic data obtained may be analyzed on a basis of the “mesomeric tautomerism” model taking into account the dynamic combination of cis- and trans-configurations. The dependence of fluorescence spectral characteristics on the solvent nature is a manifestation of intermolecular H-bond interactions.

Exciton luminescence of 8-azasteroid microcrystals

Luminescence of microcrystals of 2,3-methoxy-8-azagon-1,3,5(10),13-tetraene-12,17-dion of the class of molecules of biologically active steroids is detected at room temperature (293 K). It represents fast fluorescence of free and self-localized excitons and prolonged phosphorescence of triplet excitons.

Phosphorescence of Enaminodicarbonyl-8-Azasteroids and Related Compounds

We present the results of the investigation of the spectral-luminescent properties of some 8-azasteroids and model compounds in ethanol solution. The absorption and luminescence spectra of these molecules have been investigated. It is shown that all the compounds under investigation have common absorption and phosphorescence spectra that are close to the corresponding spectra of the related enaminodycarbonyl compounds. The results obtained allow to conclude that the main channel of singlet state deactivation is the intersystem crossing. It has been found that the 8-azasteroids are unstable under laser irradiation.

Phosphorescence of 8-Azasteroid in Solid Solution

This paper presents the results of the investigation of delayed luminescence of 2,3-methoxy-8-azagona-1,3,5(10),13-tetraene-12,17-dione classed with 8-azasteroids in ethanol solution at 77 K. Dual phosphorescence with maxima in the region of 400 and 500 nm, depending on the excitation wavelength, has been discovered. It is shown that the short-wavelength luminescence is due to the radiation transition from second triplet state. The possible mechanisms of emergence of dual phosphorescence in the compound investigated are considered.

ANGULARLY ALKYLATED 8-AZA-D-HOMOGONANES

We have established that cyclic azomethines (1-alkyl-substituted 3,4-dihydroisoquinolines) enter into the annelation reaction with cyclic β-triketones (2-acyl-1,3-cyclohexanediones) with formation of C-9 angularly alkylated 8-aza-D-homogonanes. We have shown that the reaction of asymmetric β-triketones (2-acetyl-5,5-dimethyl-4-methoxycarbonyl-1,3-cyclohexanedione) is accomplished regioselectively, leading to the 17-methoxycarbonylated 8-aza-D-homogonane derivative, existing in solutions in the form of a mixture of stereiosomers with respect to C-17 (due to keto-enol tautomerism) and in crystals in the form of a single stereoisomer. The structure of the 8-azo-D-homogonanes has been proven by UV, IR, and PMR spectra.

Annelation of 3,4-Dihydroisoquinolines with 3-Acylthiotetronic Acids: Synthesis and Properties of 8-Aza-16-thiagona-12,17-diones and 3,4-Dihydroisoquinolinium 3-Acetylthiotetronate

Abstract8-Aza-16-thiagona-12,17-diones have been obtained by the annelation of C(1)-unsubstituted 3,4-dihydroisoquinolines with 3-acylthiotetronic acids on refluxing in glacial acetic acid. The condensation of 1-methyl-3,4-dihydroisoquinoline with 3-acetylthiotetronic acid stopped at the salt formation stage. From the results of H/D isotopic exchange of 3,4-dihydroisoquinolinium 3-acetylthiotetronate it follows that a tautomeric equilibrium is established for the anion of 3-acetylthiotetronic acid, involving the protons of the acetyl group and the C(5) methylene group of the thiolactone ring in isotopic exchange.

Electronic Structure of Immunoactive Molecules of 8–Azagona–12,17–Dione

Using the semiempirical method of partial neglect of differential overlap (PNDO), we have calculated the wave functions, energies, orbital configurations of electronic states, oscillator strengths of transitions, electronic density distributions, and dipole moments for the molecule of biologically active 8–azagona–12,17–dione, containing a conformationally rigid α–acyl–β–aminovinylcarbonyl fragment. It has been established that as to their orbital nature the excited lower and higher singlet electronic states of this molecule are of the nπ*– and ππ* type respectively. The results of the theoretical analysis are in good qualitative agreement with the spectral data on absorption and luminescence. The calculations of the intermolecular interaction of the compound under consideration with a medium show that the molecular systems under consideration can possess a dynamic multicenter structure.

Luminescence Properties of 8-azasteroid Molecules

The chemical and biomedical studies of steroid heterocyclic analogs have arisen with the purpose of separation of unfavourable hormonal (influence on mineral and carbohydrate interchange) and valuable physiological (antiinflammatory, antishock, antiallergen action) effects intrinsic for steroids. Our investigations in this field [1, 2] have shown that 8-azasteroids represent themselves a new class of low-molecular non-antigenic agents to modulate immune functions of man and animals. The 8-azasteroids are highly similar in their biological action to some natural agents which responsible for co-operative intercellular interactions, in particular interactions of lymphoid cells during immune response. Studies of photophysical and photochemical properties of 8-azasteroids are important from the standpoint of revealing the interrelations between the spectroscopic properties of the molecules and their biological activity such as the immune response modulation. The characteristic feature of immunomodulating properties of 8-azasteroids is the occurrence of cross-linked, conformationally restricted N8-C14=C13(-C12=O)-C17=O aminovinyldicarbonyl fragment (1) in their structure. The object for spectroscopic investigations in this report is 2, 3-dimethoxy-8-azagona-l, 3, 5(10), 13-tetraene-12, 17-dione (1), known as an immunodepressant [1].

Synthesis and Properties of 12(E)-Ethoxyimino Derivatives of 8-Aza-16-thiagona-12,17-diones

The reaction of 8-aza-16-thiagona-1,3,5(10),13-tetraene-12,17-dienes with ethoxyimine in dimethyl sulfoxide yields the corresponding 12(E)-ethoxyimino derivatives. The physicochemical properties of these compounds were studied.

Luminescence of microcrystals and solutions of 8-azagona-1,3,5(10), 13-tetraene-12,17-dione

Abstract We present the results of the investigation of delayed luminescence of 2,3-methoxy-8-azagona-1,3,5(10),13-tetraene-12,17-dione (8,9-dimethoxy-1,2,3,5,6,10b,11,12-octahydrocyclopentane[5,6]pyrido[2,1-a]isoquinoline-1,12dione) in solid solutions. Dual delayed luminescence with maxima in the region of 400 and 500 nm depending on the excitation wavelength has been revealed. It is shown that the observed delayed luminescence is a phosphorescence of individual molecules of the substance (short-wavelength luminescence) and molecular pairs (long-wavelength luminescence) resulting from the dipole–dipole (Coulomb) interaction of strongly polarized molecules. The conclusion has been drawn that the spectral features observed for the solutions of 8-azasteroids are due to both individual molecules and their aggregates.