Agnes Gottsegen

Synthesis of homoisoflavanones—II : Constituents of Eucomis autumn alis and E. Punctata☆

Abstract The synthesis of punctatin ( 1 ). (±)-3,9-dihydro-punctatin ( 3 ). 4′-O-methylpunctatin ( 2 ). (±)-4′-O-methyl-3,9-dihydropunctatin ( 4 ). eucomnalin ( 9 ). (±)-3.9-dihydroeucomnalin ( 10 ). 4′-demethyleucomin ( 11 ) and (±)-4′-demethyl-5-O-methyl-3,9-dihydro-eucomin ( 12 ) are described and a novel alkali-catalysed ring-isomerization is reported.

Synthesis of sophorol, violanone, lonchocarpan, claussequinone, philenopteran, leiocalycin, and some other natural isoflavonoids by the oxidative rearrangement of chalcones with thallium(III) nitrate

Isoflavones are conveniently prepared by the oxidative rearrangement of 2′-hydroxy- or 2′-acetoxy-chalcones with thallium(III) nitrate in methanol into 1-(2-hydroxyphenyl)-3,3-dimethoxy-2-phenylpropan-1-ones [e.g.(46)] followed by cyclisation, and the following natural isoflavonoids were synthesised in this way: the isoflavanones sophorol (49) and violanone (68), the isoflavans vestitol (57), duratin (58), mucronulatol (59), laxifloran (60), and Ionchocarpan (61), the isoflavan quinones mucroquinone (66) and claussequinone (67), the pterocarpans philenopteran (69), leiocalycin (54), and 2-hydroxy-3-methoxy-8,9-methylenedioxy-6a,11a-dihydropterocarpan (56).Acid catalysed cyclisation of 1-(2-hydroxy-4-methoxyphenyl)-2-(2-hydroxy-4,5-methylenedioxyphenyl)-3,3-dimethoxypropan-1-one (48) gave no isoflavone but the two tetracyclic compounds, (53)(a derivative of 2-methoxypterocarp-6-ene) and (52)(a benzofuro[2,3-b][1]benzopyran).Claussequinone (67) was rapidly formed by autoxidation of its hydroquinone precursor (64), suggesting that oxidation may also have occurred during the isolation of the metabolite.

Lipase-catalyzed kinetic resolution of (±)-2-hydroxymethyl-1,4-benzodioxane

Abstract Who hath his life from rumours freed, Whose conscience is his strong retreat; Whose state can neither flatterers feed, Nor ruin make accusers great; Who God doth late and early pray More of His grace than gifts to lend; And entertains the harmless day With a well chosen book or friend; This man is freed from servile bands Of hope to rise, or fear to fall; Lord of himself, though not of lands; And have nothing, yet hath all. (Sir Henry Wotton, 1568–1639) In memory of G. Snatzke The title compound has been kinetically resolved in a lipase-catalyzed transesterification with vinyl acetate in organic solvents. The influence of the enzyme source as well as the character of the solvent on the enantioselectivity has been studied.

The synthesis of riccardin C

Abstract The macrocyclic bis(bibenzyl) riccardin C, isolated from Riccardia multifida was synthesized in an unambiguous way by Ni(O) assisted intramolecular aryl-aryl bond formation from a diiodobenzoate as the key step.

Total syntheses of riccardins A, B, and C, cytotoxic macrocyclic bis(bibenzyls) from liverworts

Di-O-methylriccardin A (3), riccardin A (1), and riccardin B (4) were synthesized by convergent schemes. Rings A and D of both riccardin A and B, as well as rings B and C of riccardin B were joined by the Ullmann ether synthesis. The aryl-aryl bond in riccardin A was established by Ni(0)-assisted intramolecular coupling of a di-iodoester (17). Rings A and B were linked in all syntheses by the Wittig reaction, whereas ring closure was effected by a tetraphenylethene catalyzed Wurtz reaction. Demethylation of (3) gave riccardin C (2).

Synthesis of some pterocarpenes obtained from Brya ebenus

The syntheses of bryacarpenes-1, -2, and -4, [4,10-dihydroxy-3,8,9-trimethoxy-(1), 10-hydroxy-3,8,9-trimethoxy-(2), and 4-hydroxy-3,9,10-trimethoxy-6H-benzofuro[3,2-c][1]benzopyran (3)], (±)-bryaflavan [(±)-3′,6,7-trihydroxy-2′,4′-dimethoxyisoflavan (33)], 4-hydroxy-3,7-dimethoxy-(18) and 3,7-dimethoxy-6H-benzofuro[3,2-c][1]benzopyran-9,10-quinone (19) is described. The quinones are not identical with bryaquinone and deoxybryaquinone, for which structures (18) and (19) had been proposed previously. In the syntheses of the pterocarpenes the novel reduction of isoflavones to isoflavan-4-ones by di-isobutylaluminium hydride was used.

Direct conversion of 2′-hydroxychalcones into isoflavones using thallium(III) nitrate: synthesis of (±)-sophorol and (±)-mucronulatol

Rearrangement of 2′-hydroxychalcones with methanolic Tl(NO3)3 followed by treatment with acid gives isoflavones.

Synthesis of the natural isoflavanones ferreirin, dalbergioidin, and ougenin

2′-Benzoyloxy-7-benzyloxy-4′,5-dimethoxy-2-methoxycarbonylisoflavone (12), prepared in nine steps by established methods, has been degraded to the corresponding phenyl benzyl ketone (9), which cyclises on treatment with ethyl formate and sodium to give 7-benzyloxy-2′-hydroxy-4′5-dimethoxyisoflavone (15); the latter has been converted in four steps into 2′,5,7-trihydroxy-4′-methoxyisoflavanone (1), identical with natural ferreirin.(±)-Dalbergioidin has been prepared by hydrogenation and subsequent saponification of 2′,4′,5,7-tetra-acetoxyisoflavone.3-Methyl-2,4,6-trihydroxyphenyl 2,4-dimethoxybenzyl ketone (21), when treated with ethoxalyl chloride, gives mainly 2-ethoxycarbonyl-5,7-dihydroxy-2′,4′-dimethoxy-6-methylisoflavone (23), which has been transformed in six steps into (±)-2′,4′,5-trihydroxy-7-methoxy-6-methylisolfavanone, (±)-ougenin (20).

Über die ringisomerisierung von isoflavonen—IX: Unwandlung von 8-methyl-genistein in 6-methyl-genistein; eine neue synthese der 2-hydroxyisoflavanone.

Zusammenfassung Die Ringisomerisierung bei Einwirkung von Kaliumathylat geht auch bei den C-Methyl-isoflavonen vor sich. Es gelang so, das 5-Hydroxy-7,4′-dimethoxy-8-methyl-isoflavon (IIIc) in 5-Hydroxy-7,4′-dimethoxy-6-methyl-isoflavon (VIIb) uberzufuhren, dessen Entmethylierung mit AlCl3 6-Methyl-genistein (VIIc) ergab.

Enantiomeric separation of racemic isoflavanones and related compounds on (+)-poly(triphenylmethyl methacrylate)-coated silica gel

(+)-Poly(triphenylmethyl methacrylate)-coated silica gel [Chiralpack OT(+)] was used for the separation of enantiomers of racemic isoflavanone, homoisoflavanone, isoflavan and 2-benzyltetralone derivatives. All the enantiomers of the above-mentioned compounds were separable. The efficiency of the separation depended on both the skeleton and substitution pattern of the racemic compounds. A relation between the number and polarity of substituents in the aromatic rings and the resolution and separation factors was observed.