The Chemical Process for the Synthesis of Methadone - Essay Example

?Methadone All drugs are primarily chemical moieties which exert their pharmacological actions by interacting with receptors inside living organisms. Methadone is a synthetic opioid developed in an endeavor to find an analgesic molecule bereft of the addictive effects of morphine. The molecule was synthesized in the 1930s by German scientists and its use as an analgesic drug as well as a means for curing opioid addiction is still prevalent. The article describes the chemical process for the synthesis of methadone. The two primary precursor’s diphenylacetronitrile and 1-dimethylamino-2-chloropropane are easily available nowadays but the basic chemical reactions involved during their manufacture are described. Synthesis of the methadone molecule from these precursors is also described. The manufacturing process yields a racemic mixture with the levo rotator form being more active pharmacologically. This synthetic drug primarily mimics morphine in its ability to act at the µ opioid receptors however with the advantage of lacking addictive potential. Introduction Drugs used for therapy in human and animal medicine may have a biological origin or may be synthesized artificially. Whatever the source, all drugs have a particular chemical structure and modifications in the structure have been attempted historically to enhance their therapeutic effect or reduce their side effects. Thus the subject of chemistry is extremely relevant to drugs used for therapy. Methadone is a prime example of a synthetic painkiller or analgesic drug which was developed by German scientists in an endeavor to develop an alternative to morphine, which had potential for addiction. The human experience of pain brought forth a need to alleviate it by artificial means and looking for natural pain killers was the first endeavor of the prehistoric man. Opium was the first substance discovered by man around third century BC which had myriad effects on the body (Gutstein & Akil, 2001). Besides alleviating pain, opium became a substance of abuse due to its profound intoxicating and euphoric effects. The active substance, morphine was isolated from opium by Serturner, who named it after the Greek god of dreams, Morpheus (Gutstein & Akil, 2001). Discovery and isolation of other alkaloids followed and these drugs were the mainstay of pain therapy during medieval times and continue to be used so in various forms as different congeners exert different pharmacological actions. During early use of these drugs, their mechanism of action was not well understood but research and discovery yielded the information that specific endogenous receptors existed inside the body to which the opioids got bound and exerted their biological actions. The receptors discovered till date have been labeled as µ, ?, ? and the latest N/OFQ receptors (Gutstein & Akil, 2001). The various congeners exert their pharmacological actions by binding with specific class of receptors. Methadone is a molecule which interacts with the µ receptors and produces profound analgesic effect as good as that of morphine. The molecule was first discovered by German scientists in the 1930s in their endeavor to find an analgesic drug without the addictive potential of morphine (CESAR). It is therefore classified as a synthetic, narcotic analgesic which has also been employed as a treatment to wean addicts away from the use of heroin which is a drug of abuse. Methadone has a longer lasting µ receptor agonist action as compared to morphine. The drug exists as an enantiomer and the l-methadone form is 8-50 times more potent as compared to the d-methadone racemate (Gutstein & Akil, 2001). Methadone is a white crystalline powder which melts at 233-236oC and is soluble in water as well as organic solvents like methanol and chloroform (drugtext.org). However, it is insoluble in ether. Methadone is available as a hydrochloride salt in its chemical form and possesses 21 carbon, 27 hydrogen, and one each of nitrogen and oxygen atoms along with the hydrochloride in its molecular structure (drugtext.org). The chemical or IUPAC name of the compound is 6-Dimethylamino-4,4-diphenyl-3-heptanone hydrochloride and the molecular formula is C21H27NO.HCl (Pharmascience). Its molecular weight is 345.91 and it has a bitter taste but no odor. Its chemical structure is shown in Fig. 1 below: Fig. 1 The Methadone Molecule (Picture Courtesy: drugtext.org) The drug is synthesized from its now easily procurable precursors, diphenylacetronitrile and 1-dimethylamino-2-chloropropane (Rhodium. 2004). The methods of chemical synthesis of the individual precursors are described below: 1. Diphenylacetronitrile: This molecule is obtained from Benzyl cyanide by an elaborate laboratory procedure depicted by the reaction shown in Fig. 2 Fig. 2 Synthetic Process for Diphenylacetronitrile (Picture Courtesy: EROWID) The above synthetic process is carried out by heating benzyl cyanide to 105-110oC and adding bromine to the heated compound. Later on benzene is added and hydrogen bromide formed during the reaction allowed to escape. After cooling the reaction mixture to 20oC, the catalyst in the form of powdered anhydrous Aluminum chloride is added. The mixture is reheated and more hydrogen bromide is formed. After this, the mixture is cooled to room temperature and poured into another mixture of ice and hydrochloric acid wherein two layers are formed and separated. The final crude product is obtained by recrystallization after exposure to sodium carbonate and sodium sulfate. 2. 1-Dimethylamino-2-Chloropropane: 1-dimethylamino-2-propanol and chloroform are mixed together in a solution and are cooled to 0oC with continuous stirring. A fresh distillate of thionyl chloride in chloroform is then added to the mixture and heated. HCl and sulfur dioxide gases are evolved during the reaction and the precipitated mixture so obtained is re-dissolved by heating. 1-dimethylamino-2-chloropropane HCl is precipitated from the boiling mixture which is cooled, diluted, filtered and recrystallized to obtain the final product. The reaction is shown in Fig. 3 below: Fig. 3: Synthetic Process for 1-Dimethylamino-2-Chloropropane (Picture Courtesy: EROWID) Synthesis of Methadone is accomplished by alkylation of the anion of diphenylacetonitrile with 1-dimethylamino-2-chloropropane, resulting in the production of the two isomeric nitriles, one with a higher melting point of 92oC which is labeled as methadone nitrile or 2,2-Diphenyl-4-dimethylaminovaleronitrile and the other with a lower melting point of 70oC which is labeled as isomethadone nitrile or 2,2-Diphenyl-3-methyl-4-dimethylaminobutyronitrile. The former nitrile (with the higher melting point), then reacts with ethyl magnesium bromide and upon subsequent hydrolysis yields methadone. The reaction yielding the racemic mixture is shown in Fig. 4 below: Fig. 4: Synthetic Process of Methadone from its 2 precursors. Conclusion Modern chemistry is an elaborate science wherein new chemical moieties are being developed as well as discovered at a high rate due to industrial and human requirements. The development of a synthetic opioid was felt as a necessity during the early half of the twentieth century in order to suffice the demand for an efficient, mass producible analgesic drug. Chemists have always endeavored to produce better molecules which involve minimal procedures utilizing raw materials which are available in plenty. Development of methadone, which is a totally synthetic opioid type drug, is one of the successes of modern chemistry. Works Cited Gutstein, H.B. & Akil, H. (2001), Opiod Analgesics, Chapter 23, Goodman & Gilman's The Pharmacological Basis of Therapeutics, Tenth Edition, McGraw-Hill, pp. 596-598 Methadone chemistry: A review, Retrieved May 1, 2011 http://www.unodc.org/unodc/en/data-and-analysis/bulletin/bulletin_1953-01-01_1_page006.html Methadone, Retrieved April 30, 2011 http://www.erowid.org/chemicals/methadone/methadone.shtml Methadone - Compound Summary, Retrieved April 30, 2011 http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=4095 Methadone, Retrieved April 30, 2011 http://www.cesar.umd.edu/cesar/drugs/methadone.asp Product Monograph, Metadol, Retrieved April 30, 2011 http://www.paladin-labs.com/our_products/metadol.pdf Physiology and Pharmacology of Methadone, Retrieved April 30, 2011 http://www.drugtext.org/library/books/methadone/section4.html#methtop Rhodium (2005). Synthesis of Methadone, Retrieved April 30, 2011 http://www.erowid.org/archive/rhodium/chemistry/methadone.html Read More