Vladimir Ovcharenko

1H and 13C NMR Study of 1‐Hydrazino‐2,3‐dihydro‐1H‐pyrazolo[1,2‐a]pyridazine‐5,8‐diones and ‐1H‐pyrazolo[1,2‐b]phthalazine‐5,10‐diones and Their Ring‐Chain Tautomerism

Treatment of 1-hydroxy-2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-diones and -1H-pyrazolo[1,2-b]phthalazine-5,10-diones with hydrazides produces corresponding acylhydrazino derivatives. In this work, ten new hydrazino derivatives were synthesized, and their properties were studied by 1H and 13C NMR spectroscopy. These compounds exhibited several types of structural variation, including ring-chain tautomerism, cis-trans isomerism with respect to the substituents in the pyrazole ring, and (E)/(Z) rotamerism with respect to the nitrogen−carbon hydrazide bond with partial double-bond character. In [D6]DMSO, 2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives were found mainly as linear tautomers, whereas 2,3-dihydro-1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives favored cyclic tautomers. For the latter compounds, a six-component equilibrium was found, consisting of a linear and of cis and trans cyclic tautomers, all of which had two rotamers, (E) and (Z). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Polyketide derivatives active against Botrytis cinerea in Gerbera hybrida

A previously isolated cDNA molecule from Gerbera hybrida (Asteraceae) codes for a new chalcone synthase-like polyketide synthase, 2-pyrone synthase (2PS). 2PS is able to synthesise 4-hydroxy-6-methyl-2-pyrone (triacetolactone), a putative precursor for gerberin and parasorboside, two abundant glucosides in gerbera. In this study, we show that gerbera plants transformed with the gene for 2PS in an antisense orientation and unable to synthesise gerberin and parasorboside are susceptible to Botrytis cinerea infection. In addition to the preformed glucosides, the transgenic plants also lack several compounds that are induced in control plants when infected with the mould. Some of these induced substances are effective in inhibiting fungal growth both in vitro and in vivo. Two of the phytoalexins were identified as the aglycones of gerberin and trans-parasorboside. The third phytoalexin is a rare coumarin, 4-hydroxy-5-methylcoumarin; however, it is typical of many plants of the sunflower family Asteraceae. The coumarin cannot be structurally derived from either gerberin or parasorboside, but may be derived from a related polyketide intermediate.

Isolation and biological activity of frankiamide

An antibiotic produced by the symbiotic actinomycete Frankia strain AiPs1 was isolated from culture broth using optimized thin-layer chromatography and high-performance liquid chromatography (HPLC) methods. The novel compound that was isolated, dubbed frankiamide, displayed antimicrobial activity against all 14 Gram-positive bacterial strains and six pathogenic fungal strains tested. The pathogenic actinomycete Clavibacter michiganensis and the ooymycete Phytophthora were especially susceptible. In addition to displaying antimicrobial activity, frankiamide also strongly inhibited 45Ca2+ fluxes in clonal rat pituitary GH4C1 tumor cells and was comparable to a frequently used calcium antagonist, verapamil hydrochloride. The results of HPLC analysis, supported by both nuclear magnetic resonance and mass spectroscopy studies, showed that frankiamide has a high affinity for Na+ ions. Journal of Industrial Microbiology & Biotechnology (2001) 27, 62–66.

Molluscicidal Activity and New Flavonoids from Egyptian Iris germanica L. (var. alba)

Abstract The molluscicidal activity of leaf and rhizome extracts of Iris germanica L. (var. alba) against Biomphalaria alexandrina snails was evaluated and the rhizome extracts were found to be the most potent. Activity-guided fractionation revealed that the chloroform extract showed the highest molluscicidal activity (LC90 = 1.26 mg/l) among the tested extracts of the rhizomes. Fraction B prepared from the chloroform extract was the most potent molluscicide (LC90 = 0.96 mg/l) in addition, it showed a significant heart rate reduction in the snail after a 6- to 24-h exposure period. It also displayed a significant level of cercaricidal potential in a time-concentration relationship pattern. Chromatographic fractionation and purification of fraction B resulted in the isolation of two novel compounds: 5,2′-dihydroxy-3-methoxy-6,7- methylenedioxyflavone and 5,7,2′-trihydroxy-6-methoxyflavanone. Their structures were established by one- and two-dimensional NMR methods and mass spectrometry

Stereospecific fragmentation processes in cycloalkane/cycloalkene-fused isomers of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives

Electron ionization-induced fragmentations were studied in a set of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives fused to either cycloalkane or cycloalkene rings, including seven pairs of cis/trans and endo/exo annelation isomers. Fragmentation patterns were confirmed by accurate mass measurements and metastable ion spectra. A number of striking differences were observed between the mass spectra of cyclohexene-fused isomers due to highly stereospecific retro-Diels-Alder (RDA) fragmentation of their M+· ions. The observed 90% stereospecificity is abnormally high in the light of the recent classification (A. Mandelbaum, 1994) of stereospecific RDA fragmentations according to the degree of substitution of the cyclohexene ring being cleaved. In the absence of RDA processes, the differences between the mass spectra of cyclohexane-fused isomers originated from heterocyclic fragmentations. The assumed mechanistic interpretation of the observed differences, e. g., in the formation of [M − C3H5O]+ ions, was consistent with the condensed-state conformations of these isomers determined previously by NMR and X-ray diffraction studies. Because of rapid RDA decompositions of their rather unstable M+· ions, the spectra of the diendo/diexo norbornene-fused isomers were virtually identical.

Molecular design of tautomeric interconversions of heterocycles

A classification and methodology of molecular design of ring—chain—ring (ring—ring) tautomeric systems by superposition of ring—chain equilibria in a structure of one molecule are considered.

5,5′,6,6′-Tetrahydroxy-3,3′-biindolyl from Beetroot (Beta vulgaris) Peel Extract

Abstract A compound of unusual structure was isolated from red beetroot (Beta vulgaris) peel extract and identified as 5,5′ ,6,6′-tetrahydroxy-3,3′-biindolyl based on the combination of NMR and MS studies.

Energy-resolved electrospray mass spectrometry of diexo-norbornane and norbornene derivatives containing a fused, phenyl-substituted, 1,3-oxazine ring: competitive retro-Diels-Alder fragmentation processes

The fragmentation behaviour of an organic ion depends on both the amount and the distribution of internal energy resulting from the ionisation process. Thus, investigations of the fragmentation pathways of complex ions can gain some advantage from energy-resolved mass spectrometry (ERMS) techniques. These methods are able to establish a relationship between the internal energy level of a precursor ion of interest and the nature and extent of the generated fragment ions. In the present study, the competitive retro-Diels–Alder fragmentation processes from norbornane and norbornene ions linked to 1,3-oxazine moieties were examined by ERMS, using an electrospray ionisation source and in-source collisional activation.

Electron ionization mass spectra of some diexo norbornane- and norbornene-fused phenyl-substituted 1,3-oxazines and related systems. Competitive retro-Diels-Alder fragmentations in 4-phenyl-4a,5,8,8a-tetrahydro-5,8-methano-4H-benzo[e]1,3-oxazines

The electron ionization spectra of seven diexo norbornane- and norbornene-fused six- and seven-membered heterocycles containing O and N in positions 1 and 3 are reported. Molecular ions of norbornane-fused oxazines, especially the 2-anilino derivative, underwent retro-Diels-Alder fragmentation leading to a cleavage of the heterocyclic ring whereas, in norbornene-fused compounds, two concurrent retro-Diels-Alder fragmentations occurred. Fragmentation patterns of norbornane-fused oxazin-2-ones(or -thiones) are closely related to each other and, in some cases, provide evidence for the presence of minor amounts of the ionized open-chain tautomers in the gas phase. The ionized molecular ions of the 2-anilino derivatives appear to exist as mixtures of 2-phenylimino and 2-anilino isomers with exo- and endocyclic C = N bonds, respectively.

Electron impact induced fragmentation of ( p-substituted phenyl)-(4′-methylphenacyl) sulfones: contribution of sulfinate ester rearrangements

The molecular ions of the title compounds are usually very unstable. The main fragmentation corresponds to the formation of p-MeC(6)H(4)CO(+) as would be expected. Another abundant fragment ion was [M - SO(2)](+) which is formed both from the original sulfone and from the rearranged sulfinate esters. There are, however, three primary ions which can be traced back to each isomeric molecular ion: p-RC(6)H(4)SO(2)(+) to the original sulfone, p-RC(6)H(4)SO(+) to the.CH(2)S(=O)O-. type sulfinate ester and p-RC(6)H(4)OH(+.) to the.CH(2)OS(=O). type sulfinate ester of which the latter seems by far to dominate. Copyright 2000 John Wiley & Sons, Ltd.