Showing papers on "Boron tribromide published in 1979"

Synthesis and biological properties of 2-, 5-, and 6-fluoronorepinephrines.

Abstract: 2-Fluoro-, 5-fluoro- and 6-fluorodimethoxybenzaldehydes were prepared by photochemical decomposition of the corresponding diazonium fluoroborates. The aldehydes were converted to the cyanohydrin trimethylsilyl ethers, which, in turn, were reduced to the dimethoxyphenethanolamines. Boron tribromide demethylation afforded the racemic ring-fluorinated norepinephrines. An alternate route, using the dibenzyloxyfluoroaldehyde, was also used to prepare 6-fluoronorepinephrine. The fluorine substituent markedly increases the phenolic acidities of these analogues. The biological properties conferred upon norepinephrine by the fluorine substituents in peripheral and central adrenergically responsive systems clearly demonstrate that 2-fluoronorepinephrine is a nearly a pure beta-adrenergic agonist, while 6-fluoronorepinephrine is an alpha-adrenergic agonist. 5-Fluoronorepinephrine retains both beta- and alpha-adrenergic agonist properties. Receptor-binding studies with specific radiolabeled ligands indicate that the specificity conferred by the site of fluorine substituents results from a change in the affinity of these analogues for the alpha- and beta-adrenergic receptors.

A simple total synthesis of (+)-ferruginol, (+)-sempervirol, and (+)-podocarpa-8(14)-en-13-one.

Abstract: The Wittig reaction of (R)-(−)-α-cyclocitral with (3-isopropyl-4-methoxybenzyl)-, (4-isopropyl-3-methoxybenzyl)-, and (3-methoxybenzyl) triphenylphosphonium chloride afforded the styryl derivatives which were partially hydrogenated to the corresponding dihydro derivatives (18, 26, and 27). Intramolecular cyclization of 18 and 26 with anhydrous aluminium chloride followed by demethylation with boron tribromide gave (+)-ferruginol and (+)-sempervirol. The similar cyclization of 27 gave (+)-13-methoxypodocarpa-8, 11, 13-triene. This was reduced with lithium in liquid ammonia in the presence of ethanol and then treated with dilute hydrochloric acid to give (+)-podocarpa-8(14)-en-13-one, a versatile intermediate for natural diterpene synthesis.

Synthesis of sequential polypeptides containing L‐β‐3,4‐dihydroxyphenyl‐α‐alanine (DOPA) and L‐glutamic acid

Abstract: Sequential polypeptides with the repeating units L-glutamyl-L-DOPA, L-DOPA-L-glutamyl-L-DOPA, L-glutamyl-L-glutamyl-L-DOPA, L-DOPA-L-DOPA-L-glutamyl-L-DOPA, and L-glutamyl-L-glutamyl-L-glutamyl-L-DOPA have been synthesized by solution polymerization of the p-nitrophenyl esters of the corresponding di-, tri-, and tetrapeptides. The O, O′-dimethyl and γ-methyl groups were used to protect side chains of L-DOPA and L-glutamic acid. The monomers for the polytripeptides and polytetrapeptides were prepared by stepwise elongation, using the dicyclohexylcarbodiimide coupling method. Moderately high molecular weight sequential polypeptides were obtained. The protected groups of the side chain were removed simultaneously by use of boron tribromide in chloroform. Trimethylphosphate-soluble sequential polypeptides containing L-DOPA were obtained.

Partial synthesis of 6'-hydroxycinchonine and its antiarrhythmic activity in mice

Abstract: The synthesis of 6'-hydroxycinchonine [8R,9S)-cinchonan-6',9-diol] was achieved by demethylating quinidine with boron tribromide in dichloromethane at -75 degrees C. The antiarrhythmic activities of 6'-hydroxycinchonine and quinidine were compared following the infusion of aconitine into the tail veins of mice to induce arrhythmias. Comparative ED50 and LD50 studies for quinidine and 6'-hydroxycinchonine revealed equivalent antiarrhythmic potencies for the two drugs but a smaller acute toxicity for 6'-hydroxycinchonine.

The Total Synthesis of (+)-Totarol and (+)-Podototarin

Abstract: The Grignard reaction of 7-methoxyphthalide with methylmagnesium iodide, followed by acetylation and dehydration, gave 3-acetoxymethyl-2-isopropenylanisole which, on catalytic hydrogenation, afforded 3-acetoxymethyl-2-isopropylanisole. This was then converted into (2-isopropyl-3-methoxybenzyl)triphenylphosphonium chloride (8) via 3-hydroxymethyl-2-isopropylanisole and 3-chloromethyl-2-isopropylanisole. The Wittig reaction of (R)-(−)-α-cyclocitral with 8 in the presence of butyllithium afforded the corresponding styryl derivative, which was converted into the dihydro compound (19) by partial catalytic hydrogenation. The intramolecular cyclization of 19 gave (+)-totaryl methyl ether (20) along with its cis-isomer. The methyl ether 20 was finally demethylated with boron tribromide to give (+)-totarol (1), which was further characterized as its acetate. Since the conversion of (+)-1 into (+)-podototarin has already been reported, the present work can be regarded as the total synthesis of natural (+)-podototarin.

Alkenylidene bisphenols, a new class of bisphenol bactericide

Abstract: Alkenylidene bisphenols are prepared by condensation of an appropriate phenol with a haloacetaldehyde, followed by base-induced elimination, or by condensation of the corresponding aryl methyl ether, elimination, and deprotection of the phenol with boron tribromide. The resulting compounds may be further elaborated by reactions on the aromatic nucleus. A series of 13 such compounds showed activity against Staphylococcus aureus; the most active was 1,1-dichloro-2-(3-allyl-5-chloro-2-hydroxphenyl)-2-(5-chloro-2-hydroxyphenyl)ethylene (16), MIC 0.16 microgram/mL. 1,1-Dichloro-2,2-bis(5-chloro-2-hydroxyphenyl)ethylene (6) was similar in its activity and spectrum to hexachlorophene.

The total synthesis of (+)-totarol and (+)-podototarin

Abstract: The Grignard reaction of 7-methoxyphthalide with methylmagnesium iodide, followed by acetylation and dehydration, gave 3-acetoxymethyl-2-isopropenylanisole which, on catalytic hydrogenation, afforded 3-acetoxymethyl-2-isopropylanisole. This was then converted into (2-isopropyl-3-methoxybenzyl)triphenylphosphonium chloride (8) via 3-hydroxymethyl-2-isopropylanisole and 3-chloromethyl-2-isopropylanisole. The Wittig reaction of (R)-(−)-α-cyclocitral with 8 in the presence of butyllithium afforded the corresponding styryl derivative, which was converted into the dihydro compound (19) by partial catalytic hydrogenation. The intramolecular cyclization of 19 gave (+)-totaryl methyl ether (20) along with its cis-isomer. The methyl ether 20 was finally demethylated with boron tribromide to give (+)-totarol (1), which was further characterized as its acetate. Since the conversion of (+)-1 into (+)-podototarin has already been reported, the present work can be regarded as the total synthesis of natural (+)-podototarin.

A simple total synthesis of (+)-ferruginol, (+)-sempervirol, and (+)-podocarpa-8(14)-en-13-one

Abstract: The Wittig reaction of (R)-(−)-α-cyclocitral with (3-isopropyl-4-methoxybenzyl)-, (4-isopropyl-3-methoxybenzyl)-, and (3-methoxybenzyl) triphenylphosphonium chloride afforded the styryl derivatives which were partially hydrogenated to the corresponding dihydro derivatives (18, 26, and 27). Intramolecular cyclization of 18 and 26 with anhydrous aluminium chloride followed by demethylation with boron tribromide gave (+)-ferruginol and (+)-sempervirol. The similar cyclization of 27 gave (+)-13-methoxypodocarpa-8, 11, 13-triene. This was reduced with lithium in liquid ammonia in the presence of ethanol and then treated with dilute hydrochloric acid to give (+)-podocarpa-8(14)-en-13-one, a versatile intermediate for natural diterpene synthesis.