1- (2,5-Dimethoxy-4-methylphenyl)-2-aminopropane
(46) (47) (48) (49)
using Me&i as a reference and the indicated solvent at ambient temperatures. Although ir and NMR data are reported only where considered significant, these spectra were determined for all reported compounds and were considered consistent with the assigned structures. Mass spectral data were obtained on a Hitachi Perkin-Elmer RMU-6E mass spectrometer. M. Simonetta and J. Favini, J. Chem. SOC.,1840 (1954). M. Morishita, S. Nakano, I. Satoda, and T. Omoto (to Nippon Shinvako Co., Ltd.), JaDan Patent 3364 (1959): Chem. Abstr., 53, 18911i (1959). P. E. Aldrich, E. C. Hermann, W. E. Meier, M. Paulshock, W. W. Prichard, J. A. Snyder, and J/ C. Watts, J. Med. Chem., 14,535 (1971). N. Kornblum, J. W. Powers, G. J. Anderson, W. J. Jones, H. 0. Larson, 0. Levand, and W. M. Weaver, J. Am. Chem. SOC., 79,6562 (1957).
Journal of Medicinal Chemistry, 1975, Vol. 18, No. 7 683 (50) J. van Dijk (to North American Philips Co., Inc.), US.Patent 3,250,803 (1966); Chem. Abstr., 65,12138d (1966). (51) D. H. Hey and J. M. Williams, J . Chem. SOC.,1527 (1951). (52) W. F. Bruce (to Wyeth Inc.), U S . Patent 2,597,446 (1952); Chem. Abstr., 47,2771i (1953). (53) A synthetic porous base anion exchange resin, quaternary amine, chloride form, was obtained from the Fisher Scientific Co., Fair Lawn, N.J. (54) Anderson Heart Perfusion Atmaratus, Metro Industries. __ Long Island, N.Y. (55) M. B. Chenoweth and E. S. Koelle, J . Lab. Clin. Med., 31,600 (1946). (56) F. F. Anderson and B. N. Craver, J. Pharmacol. Exp. Ther., 93, 135 (1948). (57) R. G. Familiar, J. R. Wardell, Jr., and L. C. Greene, J. Pharm. Sei., 56,768 (1967). (58) M. W. Nott and C. Raper, Br. J . Pharmacol., 44,589 (1972).
N-Hydroxylation of l-(2,5-Dimethoxy-4-methylphenyl)-2-aminopropane by Rabbit Liver Microsomes J. Gal, L. D. Gruenke, and N. Castagnoli, Jr.* Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, S a n Francisco, California 94143. Received November 4, 1974 Metabolic N-hydroxylation of the potent psychotomimetic amine 1-(2,5-dimethoxy-4-methylphenyl)2-aminopropane ( 5 ) by rabbit liver microsomal preparations has been investigated. Synthetic hydroxylamine 8 was obtained by sequential reduction of the corresponding nitropropene 10 with sodium borohydride followed by zinc reduction of the resulting nitropropane 11. Compound 8 in water (pH 7.4) was rapidly air oxidized to oxime 12; this oxidation was completely blocked by’rabbit liver microsomes. Microsomal incubations of amine 5 or its bis(methoxyd3)hexadeuterio analog 5-d6 resulted in the formation of 8 and %de, respectively, identified as their bis(trifluoroacetyl) derivatives by GLC-MS. Quantitative estimations of metabolite formation employing selected ion monitoring with the aid of an accelerating voltage alternator were accomplished by stable isotope dilution analyses with 5-ds as substrate and 8-do as internal standard. Similar analyses starting with “pseudoracemates” (R)-5-do:(S)-5-d6 or ( R ) 5-ds:(S)-5-d0 as substrates established metabolite 8 to be enriched with its R enantiomer.
The metabolic N-hydroxylation of aromatic amines, a reaction thought to be involved in the carcinogenic and other toxic effects of some aromatic amines, has been investigated extensively.’ Recently, interest in metabolic Nhydroxylation has been extended to aliphatic amines.2 The in vitro2a~b~g and in vivoZf N-hydroxylation of amphetamine (1) has been studied by several groups.2b,C,gIt has been suggested3 that phenyl-2-propanone (3), a major urinary metabolite4 of amphetamine in man and several other species, may arise, in part, via the oxime 2 (eq 1). However, the
S
R 1 4
5 5d3 5-d,
R
R,
R1
R.
R
H H H
H OH
H
H H COCFj CO CF, H H OH OCOCF, OH OCOCF,
H H OCH, OCH, OCD, OCH, OCD, OH OCH, OCH, OCH, OCD, OCD,
H H CH, CD3 CHj CHj CH, CHj CH, CH CH, CH, CH,
H H OCH, OCH, OCD, OCHj OCDj OCH, OH OCH, OCH, OCDj OCDi
H
H
3 5-TFA H mode of formation of oxime 2 is a matter of controversy. 5-d6-TFA H Beckett and his coworkers have suggested that 2 arises 6 H from hydroxylamine 4 (a metabolite of 1) via nonenzymatic 7 H oxidation, while Hucker and his group have p r o p o ~ e d ~ g , ~ ~ 8 H other pathways to oxime 2. Indeed, it has been claimed 8-TFA COCF, (4) is formed in incut h a t * g ~no~ N-hydroxyamphetamine ~ ad, H bations of 1 with rabbit liver microsomes under conditions Bd,-TFA COCF, where others2b,creport N-hydroxylation. These inconsistencies may be partly due to the instabilidroxylation than the S enantiomer (S)-l.This metabolic ty of aliphatic N- hydroxy compounds, especially when stereoselectivity, although described without detailed evisubjected to basic conditions in the presence of o ~ y g e n ~ ~dence, ,~ is interesting in view of the greater CNS stimulant (see below). Metabolic studies2b by Beckett and AI-Sarraj activity of (S)-(+)-amphetamine.6 Benington and his coon the influence of the chiral center of amphetamines on workers found’ that replacement of the amino group in a N-hydroxylation have shown that (R)-(-)-amphetamine series of 1-phenyl-2-aminopropanesby the hydroxylamino [(R)-1] is about eight times better as a substrate for N-hygroup decreases but does not abolish the central stimulant 2
684 Journal of Medicinal Chemistry, 1975, Vol. 18, N o 7
effects of this series of compounds. However, this activity may be due to the parent amine which may be formed in vivo by the reduction of the N - hydroxy compounds.2a Our interest in the relationship between metabolism and psychotomimetic activity of 1-phenyl-2-arninopropane derivatives has led us to investigat,e the in v i t r 0 ~ 3and ~ in vivog*lometabolism of 1-(2,5-dimethoxy-4-methylphenyl). 2-aminopropane ( 5 ) , a potent psychotomimetic amphetamine derivative.ll Metabolites resulting from oxidative attack a t the aromatic methyl g r ~ u p , ~O-demethylatioa,8 J@ and oxidative deaminationgJ@have been found. The factors governing the steric course of the metabolism of amine 5 have been under investigation, since it has been reported12 that ( R ) - 5 but not ( S ) - 5is the psychoactive species. We have found that ( R ) - 5 is excreted in the urine of rabbits treated with ruc-5 to a greater extent than is ( S G ' O and that ( S ) - 5is metabolized by rabbit liver 10,000g siipernatant fractions incubated with rac-5 to a greater extent than its a n t i p ~ d e .In ~ addition, incubation of ruc-5 with the above rabbit liver preparations leads to the stereoseiective formation of the two 0-demethylated metabolites 6 and 7, both enriched in their S enantiomer.8 In order to further characterize the oxidative metabolic pathways of 5 we have examined the in vitro formation of the two enantiomeric N-oxidation products, ( R ) - 8 and ( S ) - 8 , in rabbit liver microsomal preparations. Chemistry. A synthetic route leading to hydroxylamine 8 has been described in the literat,ure.13 The procedure illvolves the condensation of 2,5-dimethoxy-4-methylbenzaldehyde (9) with nitroethane, followed by catalytic hydrogenation of the resulting nitropropene 10. The last step in this sequence gave a complex product mixture and a low yield (8%) of the desired compound 8. An alternative route to 8 would be the lithium aluminum hydride reduction of 10, but this reaction is expected to give a substantial amount of the primary amine 5 as side product.14,+We now wish to report an alternative synthesis of 8 (Scheme I ) which is applicable to a variety of 1-phenyl-2-hydroxyamin ~ a l k a n e s and l ~ ~ which gives re'sonable yields of 8 free of side products. Scheme I. Synthesis of 8
@'" CH 0
NaBH,
CH
@'"
~
(:H O H T H F
cH
CH OCH 10
'
NO.
OCH 11
Table I . Gas Chromatographic C'haracteristics of %'ITA and Related Compounds Coinpouiid Ret ent i o 11 iiinc. I i i i i i
13 3.0"
.. .
crease 2' niin. 5 2 1 3 1 ~h. 2f'l(iw 30 m i
.
14 11.5" ...
S-'I'FA 5-TFA 4"9.*2.6!' 4 . 3 b . -
.-
11
5.0" -
teniperatiire program. initial 128" 111:30mi min. 'lCuritiirions 3% Oi'. 1. i ~ o r h e r n i s l inin.
possible side reacti(~iis.1~'t'.'.d.16 However, by carefully U J ~ I trolling the reaction conditions (see Experimental Section) the side reactions can be minimi~ed,'5"~:and in our hands the reduction of 10 proceeded smoothly to gibe a good yield of 1 1 . Reduction of 11 to the desired hydroxylamine 8 was accomplished using zinc powder in aqueous tetrahydrofur an (THI?) containiiig ar1imonirim c~l~loritle.'~ Siiice zinc powder can reduce hydroxylamines to amirics,'
