N. D. Pokhilo

Chemistry of naphthazarine derivatives: XIV. Preparative synthesis of 1′-bromoalkylnaphthazarines

A reaction of alkylnaphthazarines with bromine in tetrachloromethane was investigated. A preparative synthesis was developed for substituted 1′-bromoalkylnaphthazarines, and based on the substance 1′-hydroxyalkylnaphthazarines were prepared, analogs of shikalkin, a racemic mixture of plant pigments from Boraginaceae family. 2-Acyl-3-hydroxynaphthazarine was synthesized, a minor metabolite of urchin from genus Echinothrix.

Cytotoxic activity of intermediates and side products of echinochrome synthesis

The cytotoxic activity of the principal intermediates and side products of echinochrome synthesis toward gametes of the sea urchin Strogylocentrotus intermedius was studied. Di-and trichloro naphthazarin derivatives with two vicinal Cl atoms were the most active.

Synthesis of lomazarin and norlomazarin, pigments from Lomandra hastilis

5,8-Dihydroxy-2,3,6-trimethoxy-7-ethyl-1,4-naphthoquinone (1) was used to synthesize in high yield 5,8-dihydroxy-7(1′-hydroxyethyl)-2,3,6-trimethoxy-1,4-naphthoquinone (lomazarin, 3), a pigment from Lomandra hastilis. Alkaline hydrolysis of lomazarin produced mainly 5,6,8-trihydroxy-2,3-dimethoxy-1,4-naphthoquinone (9) through a retro-aldol decomposition of the 6-keto-form of 5,6,8-trihydroxy-7(1′-hydroxyethyl)-2,3-dimethoxy-1,4-naphthoquinone (13b) formed during the reaction. 2,5,8-Trihydroxy-7(1′-hydroxyethyl)-3,6-dimethoxy-1,4-naphthoquinone (norlomazarin, 4a), a pigment of L. hastilis, and its 3,5,8-trihydroxy-7(1′-hydroxyethyl)-2,6-dimethoxy isomer 4b were formed as a difficultly separable mixture in addition to quinone 9.

Chemistry of naphthazarin derivatives. 11. Trisubstituted hydroquinone derivatives in the preparative synthesis of naphthazarins

The Friedel—Crafts acylation of trimethylhydroquinone, 3,5-diethyl-2-hydroxyhydroquinone, and 3,5-diethyl-1,2,4-trimethoxybenzene with dichloromaleic or citraconic anhydride in an AlCl3—NaCl melt is accompanied by o-C-dealkylation to afford functionally substituted naphthazarins.

Chemistry of naphthazarin derivatives. 9. Direct observation of prototropic tautomerism of (poly)hydroxynaphthazarins by IR spectroscopy

A series of substituted (poly)hydroxylated naphthazarins (5,8-dihydroxy-1,4-naphthoquinones) were synthesized. In general, (poly)hydroxynaphthazarins exist in organic aprotic solvents as mixtures of tautomeric 1,4-naphthoquinonoid forms (IR data). The ratio of tautomers was determined for the first time. The effects of the nature of substituents and the solvent polarity on the tautomeric equilibrium were qualitatively estimated.

Simple Synthesis of Spinochrome C, a Sea-Urchin Pigment

3-Acetyl-2,5,6,7,8-pentahydroxy-1,4-naphthoquinone (3-acetyl-2,6,7-trihydroxynaphthazarine, spinochrome C, 1a) is a sea-urchin (Class Echinoidea) metabolite [1]. Spinochrome C in addition to other classic quinoid pigments from this animal class is a potent antioxidant [2]. Known approaches to the synthesis of spinochrome C typically require several steps and give low yields [3]. We found that bromination of the relatively available dimethyl ether of echinochrome (2) [4] by Br2 in CCl4 containing H2O formed the dimethyl ether of spinochrome C (3) (30% yield) (Scheme 1). Compound 3 was probably a hydrolysis product that formed during the reaction of gem-dibromide 4. Heating diether 3 with conc. HBr (90°C) gave spinochrome C (1a, 40%) and its deacylation product spinochrome D (2,6,7-trihydroxynaphthazarine, 1b, 40%). A similar conversion (1a 1b) was reported before [5].

Synthesis of 6,8,9-Trihydroxy-2-Methyl-2H-Naphtho [2,3-b]Pyran-5,10-Dione, a Pigment of Echinothrix diadema, and Its Analogs

6,8,9-Trihydroxy-2-methyl-2H-naphtho[2,3-b]pyran-5,10-dione, a pigment of Echinothrix diadema, was synthesized. It existed as a mixture of two tautomers in CHCl3 solution according to IR spectroscopy. Its analogs 6,9-dihydroxy-2-methyl-2H-naphtho[2,3-b]pyran-5,10-dione and 6,9-dihydroxy-2-methyl-7,8-dichloro-2H-naphtho[2,3-b]pyran-5,10-dione were synthesized.

Chemistry of Naphthazarin Derivatives: XV.* Bromination of Naphthazarin and Its Derivatives

Bromination of a number of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives having different substituents in the aromatic ring with molecular bromine in carbon tetrachloride was studied. Preparative procedures for the synthesis of 2-bromo-5,8-dihydroxy-7-methoxy-1,4-naphthoquinone, 2-bromo-6,7-dichloro-5,8-dihydroxy-1,4-naphthoquinone, 2-bromo-3,5,8-trihydroxy-1,4-naphthoquinone, and 2-bromo-6,7-dichloro-3,5,8-trihydroxy-1,4-naphthoquinone were developed.

Chemistry of naphthazarin derivatives. 12. Synthesis and investigation of prototropic tautomerism of 3-(alk-1-enyl)-2-hydroxynaphthazarins

Substituted 3-(alk-1-enyl)-2-hydroxynaphthazarins were synthesized. According to data from IR spectroscopy, these compounds exist in organic aprotic solvents as mixtures of tautomeric 1,4-naphthoquinonoid forms. The compositions of tautomeric mixtures were quantitatively determined. The effects of the structure of the alkenyl substituent and the polarity of the solvent on the tautomeric equilibrium were qualitatively estimated.

New triterpenes from the leaves of Betula pendula and Betula ermanii

Continuing a study of the chemical composition of the leaves of one of the birch species most widely distributed in the Soviet Union (Betula pendula Roth. [i]) we have analyzed the unsaponifiable part of an ethereal extract of leaves gathered in June, 1985, in the environs of Minsk. The following triterpenoids have been isolated and identified (% on the weight of the air-dry leaves): betulafolienetriol) 0.09; dammar-24-ene-3a,12B,17~,20(S)tetraol) 0.08; betulafolienetriol oxide) 0.015; dammar-24-ene-3~,17a,20(S)-triol) 0.01; dammar-25-ene-3a,12B,17~,20(S),24(g)-pentaol) 0.03 [i]; and a triterpene (I) with mp 278280°C (acetone) not previously isolated from plant materials.