Manufacturing Process
A solution of 3,4-dimethylpyridine was added to a methyliodid. Then to the resulting solution containing 1,3,4-trimethylpyridinium iodide the 4methoxybenzylmagnesium chloride was added. After reaction process the 1,3,4-trimethyl-2-(4-methoxy-benzyl)-pyridine was obtained.
To the solution of 1,3,4-trimethyl-2-(4-methoxy-benzyl)-pyridine was reduced by hydrogen over 10% palladium-on-charcoal, and when reduction was complete, the catalyst was removed by filtration and the filtrate taken to dryness. The residue was recrystallized to give 2-(4-methoxybenzyl)-1,3,4trimethyl-1,2,5,6-tetrahydropyridine.
To the 2-(4-methoxybenzyl)-1,3,4-trimethyl-1,2,5,6-tetrahydropyridine the solution of hydrobromic acid was added and heated under reflux.The product obtained was recrystallized and yield N-methyl-1,2,3,4,5,6-hexahydro-6,11dimethyl-8-hydroxy-2,6-methano-3-benzazocine (2'-hydroxy-2,5,9trimethylbenzo-6-morphen), which then was demethylated by bromcyan (BrCN). As a result the racemic cis-1,2,3,4,5,6-hexahydro-6,11-dimethyl-8hydroxy-2,6-methano-3-benzazocine was obtained (that is a. 2'-hydroxy-5,9dimethyl-6,7-benzomorphen).
A mixture of 8.7 g racemic cis-1,2,3,4,5,6-hexahydro-6,11-dimethyl-8hydroxy-2,6-methano-3-benzazocine, 6.0 g of 1-bromo-3-methyl-2-butene, 5.0 g of sodium bicarbonate, and 125 ml of N,N-dimethylformamide was stirred and refluxed for approximately 4.5 hours. The reaction mixture was then filtered, and the solid on the filter was washed with ethanol. The filtrate and the wash liquor were combined, concentrated under reduced pressure, and then extracted with chloroform. The chloroform extract was concentrated under reduced pressure to yield a syrup which weighed 15.8 g. This syrup was dissolved in 120 ml of diethyl ether and the resulting solution was filtered to remove approximately 0.5 g of a brown amorphous solid. The filtrate was extracted with a mixture of 5 ml of concentrated hydrochloric acid and 20 ml of water. To the extract there was added 5 ml of concentrated ammonium hydroxide solution and ice. A pale tan syrup separated from solution and after stirring, this syrup solidified. The resulting pale tan solid was collected and dried; it weighed 10.6 g. After two recrystallizations from a mixture of methyl alcohol and water, with charcoaling, the 1,2,3,4,5,6-hexahydro-3-(3-methyl-2butenyl)-6,11-dimethyl-8-hydroxy-2,6-methano-3-benzazocine weighed 8.2 g and melted at 145°-147°C.
The1,2,3,4,5,6-hexahydro-3-(3-methyl-2-butenyl)-6,11-dimethyl-8-hydroxy2,6-methano-3-benzazocinewas soluble in a mixture of 0.35 ml of 2 N hydrochloric acid and 0.15 ml of water to the extent of 10%, the pH of the 1% solution being 2.80; and when the pH of the 1% solution was gradually raised by addition of 10 N sodium hydroxide solution, a precipitate formed at pH 5.4. The 1,2,3,4,5,6-hexahydro-3-(3-methyl-2-butenyl)-6,11-dimethyl-8hydroxy-2,6-methano-3-benzazocine hydrochloride melted at 245°-247°C, dec.
General Description
The benzomorphans are prepared synthetically and thus resultin several stereoisomers. The active benzomorphans arethose that have the equivalent bridgehead carbons in thesame absolute configuration of morphine (carbons 9, 13,and 14 of morphine). The only benzomorphan in clinical useis pentazocine, which is prepared as the 2(R), 6(R), 11(R)enantiomer (Chemical Abstracts numbering). Pentazocineis a mixed agonist/antagonist displaying differing intrinsicactivity at the opioid receptor subtypes. At the κ-receptor,pentazocine is a partial agonist and a weak antagonist.
According to the manufacturer, a 50-mg dose of pentazocinehas about the same analgesic potency as 60 mg of codeineand about 1/50th the antagonistic activity of nalorphine.74Pentazocine is also an agonist at the κ-receptor, and thismay be responsible for the higher percentage of patients thatexperience dysphoria with pentazocine versus morphine.75Some evidence also exists that women respond better to κ-agonists than men. Pentazocine is available in a 50-mgtablet along with a low dose of the antagonist naloxone 0.5mg (Talwin NX). Naloxone 0.5 mg orally is expected tohave no pharmacological effect but is included to dissuadeIV drug abusers from dissolving and injecting Talwin NX.
