Vladimir P. Zaytsev

Aromatization of IMDAF adducts in aqueous alkaline media

In this paper, we propose a simple synthesis of isoindoline-4-carboxylic acids by means of the aromatization of 3a,6-epoxyisoindoles in alkaline media. The method is facile from an experimental point of view: a short-term (0.5–2h) reflux of epoxyisoindoles in 5% aqueous solutions of alkali leads to the target products in 40–90% yields. The absence of by-products, ease of isolation of the target products and applicability to acidophobic group bearing substrates favorably distinguishes the proposed procedure from previously utilized acid-catalyzed methods. The proposed strategy has been successfully utilized for isoindole containing compounds and nuevamine-type alkaloids.

2-Benzazepine Nitrones Protect Dopaminergic Neurons against 6-Hydroxydopamine-Induced Oxidative Toxicity

A number of C‐3 spirocyclic 2‐benzazepine analogs of α‐phenyl‐N‐tert‐butyl nitrone (PBN) were synthesized and tested for their activity in protecting rat brain mitochondria and dopaminergic (DA) neurons against 6‐hydroxydopamine (6‐OHDA), a toxin inducing destruction of the DA nigro‐striatal pathway in rodent models of Parkinsons disease. The newly synthesized nitrone derivatives were firstly investigated for their activity in decreasing the level of hydroxyl radicals generated during 6‐OHDA oxidation, and inhibit lipid peroxidation (TBARS assay) and protein carbonyl content (PCC) in rat brain mitochondria. Most of the studied 2‐benzazepine nitrones showed inhibitory potencies in both TBARS and PCC assays at least two magnitude orders higher than that of PBN. The data obtained usefully complemented the known structure–activity relationships. In particular, 5 and 10, bearing C‐3 spiro cyclopentyl and tetrahydropyranyl moieties, respectively, at 8 µM concentration proved to be significantly more effective than PBN in protecting cultured DA neurons exposed to 6‐OHDA, which alone causes about 45% cell loss in 24 h. In addition, we found that 5 inhibited butyrylcholinesterase with an IC50 value of 16.8 µM, which would enhance its potential as neuroprotective agent in Alzheimers neurodegeneration. These findings extend the utility of benzazepine‐based PBN analogs in the treatment of age‐related free radical‐mediated disorders.

Cycloaddition of furfurylamines to maleic anhydride and its substituted derivatives

The regio- and stereoselectivity of the [4 + 2] cycloaddition of maleic, citraconic, dichloromaleic, and dibromomaleic anhydrides to difurfuryl amines and secondary furfurylamines were studied. N-Furfuryl-, N-phenyl-, and N-benzylhexahydrooxoepoxyisoindole-7-carboxylic acids were synthesized. An approach was developed for obtaining hexahydroepoxyoxoisoindole-7-carboxylic acid unsubstituted at the nitrogen atom. Aromatization of the oxabicycloheptene fragment of the dihaloepoxyiso- indolonecarboxylic acids gave a series of 7-carboxy-2-R-isoindol-1-ones.

Inter­action between maleic acid and N-R-furfuryl­amines: crystal structure of 2-methyl-N-[(5-phenyl­furan-2-yl)meth­yl]propan-2-aminium (2Z)-3-carb­oxy­acrylate and N-[(5-iodo­furan-2-yl)meth­yl]-2-methyl­propan-2-aminium (2Z)-3-carb­oxy­prop-2-enoate

The molecular and crystal structures of two N-(furylmethyl)propan-2-aminium salts – the products of interaction between maleic acid and N-R-furfurylamines – were studied by X-ray diffraction and correlated with their lack of reactivity in [4 + 2] cycloaddition reactions.

Ring-chain tautomerism in the products of the reaction between 5-substituted furfurylamines and anhydrides of α,β-unsaturated carboxylic acids

The reactions of 5-substituted furfurylamines with anhydrides of α,β-unsaturated carboxylic acids (acryloyl chloride and maleic anhydride) were studied. The first step of the reaction mechanism involved acylation of furfurylamine nitrogen atom, followed by a stereospecific, spontaneous intramolecular Diels–Alder reaction at the furan ring of the N-furfurylamide intermediates. When the starting materials were 5-alkyl-substituted furfurylamines, the expected 1-oxo-2,3,7,7a-hexahydro-1H-3a,6-epoxyisoindoles or the corresponding 7-carboxylic acids were obtained in up to 98% yields. The acylation of 5-aryl-substituted furfurylamines with maleic anhydride led to N-furfurylmaleic amides, which formed a dynamic equilibrium in solutions with adducts formed by intramolecular [4+2] cycloaddition, 3a,6-epoxyisoindole-7-carboxylic acids, as proved by NMR spectroscopy. X-ray structural analysis results show that these mixtures crystallized in the form of the cyclic tautomer.

Wagner–Meerwein rearrangement in 2,6a-epoxyoxireno[e]isoindole series

A cation-catalyzed Wagner–Meerwein skeletal rearrangement in octahydro-2,6a-epoxyoxireno[e]isoindole series was studied. It was shown that the reaction proceeds ambiguously when effected by boron trifluoride etherate in acetic anhydride: the target 4,5-bis(acetoxy)-4,6-epoxycyclopenta[c]pyridines as well as the products of their further degradation, cyclopenta[c]pyridines, were isolated from the reaction mixture in 10–15% yields as single diastereomers.

Synthesis of furyl-, furylvinyl-, thienyl-, pyrrolinylquinazolines and isoindolo[2,1-a]quinazolines

A method for the synthesis of hydrogenated furyl-, furylvinyl-, thienyl-, and pyrrolinyl-substituted quinazolin-4-ones was developed. A possibility of the reaction of 2-furylquinazolines with maleic anhydride was demonstrated. A number of quinazolines obtained were subjected to a primary bioscreening on inhibition of acetylcholinesterase.

Synthesis of Epoxyisoindolo[1,2-a]isoquinolinium Salts by an Intramolecular [2+4] Cycloaddition Reaction in 2-Allyl-1-furylisoquinolinium Halides

We examined the tandem alkylation/[2+4] cycloaddition of 1-(2-furyl)-3,4-dihydroisoquinolines by various allyl halides. It was found that the process occurred through the intermediate formation of 2-allyl-1-furyl-3,4-dihydroisoquinolinium salts with a subsequent intramolecular exo addition of the allyl fragment to the furan ring. The adducts obtained were structural analogs of the isoindolo-[1,2-a]isoquinoline alkaloids jamtine and hirsutine.

Methyl 4,5-diacet­oxy-1-oxo-2-phenyl­perhydro-4,6-epoxy­cyclo­penta­[c]pyridine-7-carboxyl­ate ethanol solvate

The title compound, the product of an acid-catalysed Wagner–Meerwein skeletal rearrangement, crystallizes as an ethanol monosolvate, C20H21NO8·C2H6O. The title molecule comprises a fused tricyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) in the usual envelope conformations and one six-membered ring (piperidinone) adopting a flattened twist–boat conformation.

Continuous-flow catalytic hydrogenation of 3a,6-epoxyisoindoles

Selective catalytic (10% Pd/C) hydrogenation of the double bond in the oxabicyclo[2.2.1]heptene fragment of substituted fused 1-oxo-3a,6-epoxyisoindoles is described. A continuous-flow hydrogenation device that incorporates in situ hydrogen generation by electrolysis of water was used. Changing the hydrogen source from water to deuterium oxide provides possibility to synthesize deuterated oxoepoxyisoindolones. Hydrogenation is stereoselective to give exclusively exo-cis deuterated derivatives.