Benzomorphans

In a continuation of the theme of simplification of the morphine ring, it was found that one of the carbocyclic rings (that which contained the allyl alcohol in morphine proper) can be dispensed with as well, to give compounds that show the full activity of the natural prototype. These agents, the benzomorphans, are of 

The key to clinical agents in this series, the secondary amine, 65, is obtained by a sequence analogous to that used to obtain desmethymorphine. Thus, the phenol (63) is first acetyl-ated (64), and then demethylated by treatment with cyanogen bromide hydrolysis gives the desired aminophenol (65). Alkylation 

Treatment of (16-3) with sodium borohydride leads to the selective reduction of the enamine bond to lead to the tetrahydropyridine (16-4). This intermediate undergoes ring closure with a strong acid to give the benzomorphan (16-5) in direct analogy to the more complex morphinans. The product consists predominantly of the isomer that bears the equatorial secondary methyl group [18], 

Alkylation of (17-5) with phenethyl bromide leads to phenazocine (18-1), a quite potent analgesic that, however, exhibits the same profile of side effects as the classical 

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A similar oxazolidine-based strategy was employed in the syntheses of R-(+)-anatabine (84) and (+)-benzomorphan (85), utilizing Zincke-derived salts 80 and 81, respectively (Scheme 8.4.26). In these cases, borohydride reduction, followed by cyclization, led to oxazolidines 82 and 83 as substrates for organometallic addition and subsequent elaboration to the natural products... 

A rather unusual reaction forms the key step in the preparation of a benzomorphan bearing a fatty side chain, The scheme used to form the benzomorphan nucleus, which is patterned after the Grewe synthesis originally developed for... 

The search for opioid analgesics which show reduced addiction liability ha.s centered largely on benzomorphan and morphinan derivatives. Some research has, however, been devoted to derivatives of the structurally simpler meperidine series. The preparation of one such compound, picenadol (59), starts with the reaction of N-methyl-4-piperidone with the lithium derivative from m-methoxybromobenzene. Dehydration of the first formed carbinol 51 gives the intermediate 52. Deprotonation by means of butyl lithium gives an anion which can be depicted in the ambident form 53. In the event, treatment of the anion with propyl bromide gives the product 54 from reaction of the benzylic anion. Treatment of that product, which now contains an eneamine function. 

The regiochemical course reacting saturated ketones depended on the substitution pattern of the a-positions. In most cases, the intermediate oxime had an anti N-OH function with respect to the chain branched a-position. Consequently, the more substituted alkyl group preferentially migrates. This advantage was utilized for synthesizing the spiro a-amino-e-caprolactam (202 203, Scheme 38) [12c], the Mexican bean beetle azamacrolide allomone (205 206, Scheme 39) [44 a], in a key step of the chiral synthesis of benzomorphanes... 

McLawhon, R.W. West, R.E., Jr. Miller, R.J. and Dawson, G. Distinct high-aff1nity binding sites for benzomorphan drugs and enkephalin in a neuroblastoma-brain hybrid cell line. Proc Natl MM USA, 78 4309-4313, 1981. 

Because the psychotomimetic benzomorphans, classed as sigma opioids, inhibit binding of 3H-PCP and show PCP-like actions in several behavioral assays, it has been suggested that PCP and sigma opioids act through the same binding sites. However, recent work by a number of investigators (Su 1982 Tam 1983 Martin et al. 

Chang, K.J., and Cuatrecasas, P. Novel opiate binding sites selective for benzomorphan drugs. J Biol Chem 254 2610-2618, 1979. 

Altura, B.T. Quirion, R. Pert, C.B. and Altura, B.M. Phencyclidine (angel dust) analogs and "sigma" opiate benzomorphans cause cerebral arterial spasm. Proc Natl Acad Sci II.SA 80 865-869, 1983. 

Omission of the phenolic group from cyclazocine results in a molecule which retains analgesic activity. In a classical application of the Grewe synthesis,15 the methylated pyridinium salt 54 is condensed with benzylmagnesium bromide. There is thus obtained the dihydropyridine 55. Treatment of that intermediate with sodium borohydride results in reduction of the iminium function to afford the tetrahydro derivative 56. Cyclization of 56 on treatment with acid leads to the desired benzomorphan nucleus. The cis compound (57) is separated from the mixture of isomers and demethylated by the cyanogen bromide procedure (58,... 

Oxidation of the benzylic methylene group in cyclazocine to a ketone is also consistent with analgesic activity. Acetylation of benzomorphan 62 affords the diacetate 63. Selective hydrolysis of the phenolic acetate (64) followed by methylation of the thus uncovered phenol affords intermediate 65. 

It has been proposed, on the basis of observations made using the benzo-morphan derivative (MR 2034) (8), that all kappa agonists may cause undesired dysophoria and even psychotomimesis in man [27]. Benzomorphans such as MR 2034 with affinity for sigma receptors are well-known to be associated with dysphoria. To date, there has been no report of a dose-ranging clinical study with a truly kappa selective agonist which describes the analgesic effects and the onset of dysphoric symptoms. 

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