4H-YYRAZINO [l,a-U]PYRI,llIDIN-4-O~~S
September 1968
the esterification reactions. h'mr speclra were recorded on the
HCI salts in dimethyl-& sulfoxide. Hydrolysis of N-Methyl-3-Piperidyl Esters of Glycolic Acids.The method of Biel and co-workers10 was employed. A 0.45-g sample ( J f the S-methyl-&piperidyl glycolate HCI (1, 2, 21, or 22, Table 11) was heated vigorously for 1 hr in 30 ml of 33To H:SOd. The cooled solution was decanted from resinous material
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and was extracted three times with ether. The aqrleotls solittion was cooled in an ice bath, made strongly alkaline with KaOH pellets, then was extract,ed repeatedly with ether. The combined ethereal extracts were dried (NandOd), and the ir spectrum was recorded. In each instance, the spectrum vas supei,impoaable upon a similar spectrum of an authentic sample of N-methyl-3piperidinol.
Chemistry and Pharmacology of a Series of Substituted 4H-Pyrazino[ 1,2-u]pyrimidin-4-ones D o x . 4 ~I,. ~ TREPANIER, L. W. RAMPY, KEXKETH L. SHRIVER, Chemistry Research Department
JOHN N. EBLE,AKD PHILIP J. SHEA ~'horvkucohyijl)epartrrkent, H u t t u n Health 1Zeseurch and L)evelopnlent Center, Y'he Doul Chel?kkcu/ Corrkpang, Z/onavi[[e,Indiuriu Received March 25, 1968
A series of X-pheiiyl-%( t,ertiary aminoalkoxy)-4H-pyrazino [ 1,2-a]pyrimiditiories obtained by condensing ethyl phenylmalonate with aminopyrazine followed by base-catalyzed 0-tertiary-amino alkylation of the resultwas screened for CSS activity in mice. Sotie ing 2-hydroxy-3-phenyl-4H-pyraxino[1,2-a]pyrimidinil-one showed significant activity in the maximal electroshock, oxotremorine, strychnine lethality, pent ylenetetrazole seizure threshold, or d-amphetamine aggregate toxicity tests. Some potentiated the effect of hexobarbital and d-amphetamine in mice and antagonized the effect of reserpine.
h sewch of the chemical literature revealed that the pyrazino [1,2-a]pyrimidine system has not been reported. In fact, the only pyrazinopyrimidine system reported is that found in the pteridines, the pyrimido[4,5-b]pyrazine heterocycle. This prompted us to undertake a synthesis and pharmacological testing study in this area. This paper reports the results of this study.
SCHEME I
I
I1
PhCH(CO0Et 160-170-
pyradino[ l,2-a]pyrimidine
pyriniido[4,5-b]pyrazine
Because our primary interest was the uncovering of new structures with central nervous system activity, 'i'hCH(CN,COOEt derivatives of the pyrazino (1,2-a]pyrimidine hetero125-140' cycle that contained a phenyl or substituted phenyl in the 3 position and a tertiary aminoalkoxy chain in the 2 position were synthesized and evaluated for CKS activity. This type of derivative was selected for synthesis because it contains a type of phenethylamine moiety and a choline or choline-like side chain which increases the likelihood it will affect the CNS neurotransmitters, norepinephrine and acetylcholine. The desired 3-pheny1-2-(tertiary aminoa1koxy)pyV VI razino [1,2-a]pyrimidin-4-ones (11) were obtained by condensing ethyl phenylmalonate with aminopyrazine followed by base-catalyzed 0-alkylation of the result(111) was obtained. That the em-amino nitrogen arid ing 2-hydroxy-3-phenyl-4H-pyrazino \1,2-a]pyrimidinnot one of the ring nitrogens was alkylated was indi+one (I) (Scheme I). cated by the pmr spectrum of 111. The vinyl proton I n order to obtain more diverse structural modificaand the DLI exchangeable proton on the exo nitrogall tions pyrazinopyrimidinone I was 0-alkylated with appeared as doublets (J = 12.5 cps) at 543 and 672 a-chloro esters and chloracetonitrile, and aminopyracps, respectively. The pmr spectrum of the alternazine was condensed with diethyl ethoxymethylenetive structure, alkylation of a ring nitrogen, wou d malonate and diethyl phenylcyanoacetate. not show a vinyl proton coupled with an exchangeable When aminopyrazine was allowed to react with diS H proton. Ring closure of I11 to 3-carboethoxy-4Hethyl ethoxymethylenemalonate neat at 110" a 63Yc pyrazino [ 1,2-a]pyrimidin-4-one (IV) was accomplished > ield of diethyl p~raziri~laniinometh~lenemalunate in S970 yield by heating I11 a t 230" in Dowtherm.
-L =
d
A
3
I-
I-
September 1968
4H-PYRAZINO [1,.)-a]PYRIMIDIN-~-ONES
3 -Carboethoxy -4H-pyrazino [ 1,2-a]pyrimi d i 11-4-o 11e (117) was allowed to react with N,S-diethylethylenediamine, phenylmagnesium bromide, and sodium @dimethylaminoethoxide in an attempt to introduce moieties that are present in known CKS active compounds. However, I V is sensitive enough to these basic reagents that in our hands these reactions all yielded intractable tars. Ethyl phenylcyanoacetate reacted with aminopyrazine to give a product tentatively assigned the structure 4-imino-2-hydroxy-3-phenyl-4H-pyrazino[ 1,2-a]pyramidine (V) based on spectral analysis of I’ and elemental and spectral analysis of its diacetate derivative VI. However, the spectral data do not exclude other protomeric forms nor do they exclude the structural isomer of 1-in which the imino group and the hydroxyl group are interchanged. Because “malonylamiiiopyrazine” has not been reported and because various structures have been formulated’ for “malonyl-a-amiiiopyridiiie,” pyrazinopyrimidinone (I) is described in the Experimental Section. The physical and spectral properties of I indicate that. similarly to “malonyl-a-aminopyridille,” it exists predominantly as the mesomeric betaine. Because of the strength of the +S-H 0- hydrogen bond, in the solid state, the betaine would most likely be irltermolecularly hydrogen bonded so that I is most accurately formulated as follows. -41~0,the precise posi-
tion of the acidic proton is a niaiter of conjecture ab it was not found in the pmr spectrum and, although the ir spectrum indicates it is certainly bonded between S and 0 , the degree of association to either 0 or Y is not indicated. Chemically, pyraziIiopyrimidiIioiie (I) differed from “malonyl-a-aminopyridine” in that it failed to give a chloride when treated with POC1, and base-catalyzed alkylation resulted in isolation of only 0-alkylated product. In contrast, “malonyl-a-aminopyridine” gives a chloride when allowed to react with POCI, arid base-catalyzed alkylation has giver1 S-alkylated or 0-alkylated products or mixtures of both.’ Pharmacology.-These pyrazinopyrimidinones w r e evaluated for C S S activity using a battery of screening methods; the data are summarized in Table I. Sone shou ed significant activity in the maximal electroshock, oxotremorine, strychnine lethality, pentamethylenetetrazole seizure threshold, or the hydrochloric acid writhing tests except 10 and 15 which were active in HC1 writhing test (EDLo’s of 31.6 arid 76.1 mg/kg, respectively). Some of the pyrazinopyrimidinones in this series showed activity in the hexobarbital sleep time test. The more active compounds (1, 9, 10, 15) were selected (1)
\ R . I i a t r i t d k \ and .\
.J iVarinq, J Chem S O L , 1544 (lYb2)
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for testing for reinductioii of sleep in hexobarbitaltreated mice. They were also active in this test which suggests a CSS rather than a metabolic mechanism of action. To determine possible antidepressant activity of these compounds they were tested for ability t o prevent reserpine-induced ptosis in mice and potentiate &hetamine toxicity in aggregated mice. When test compounds were given intraperitoneally 30 min before reserpine (1 m g k g ) and the mice checked for presence or absence of ptosis 45 min after the reserpine, ptosis was absent only in the group of mice that had been pretreated with 6. However, when the test compounds were given 3 hr before reserpine, 6, 8, 10. 17, and 18 all prevented ptosis. Thus four compounds that were inactive when administered 30 min prior to reserpine mere active in the delayed test. Compounds 1, 4, 6, and 10 potentiated d-amphetamine toxicity in aggregated mice. In summary, this series of pyrazinopyrimidinones shows some CNS activity which is manifested in potentiating the effect of hexobarbital and d-amphetamine in mice and antagonizing the effect of reserpine. I n these three tests some of these compounds behaved similarily to the antidepressants imipramine and amitriptyline. Experimental Section The melting points were ohtained in an opeti capillary t ube with the Thomas-Hoover Uni-3Ielt and are rincorrected. The elemental analyses were done by Midwest hlicrolabs., Inc., Indianapolis, Ind. The pmr spectra were ohtained a t 60 n l c with a Varian A-60 spectrophotometer, for 10% CIIC13 or saturated do-DRISO solutions containing T M S as an internal standard. I r spectra were obtained with a Perkin-Elmer 337 grating spectrophotometer. Uv spectra were scanned on the Cary recording spectrophotometer AIodel 15 in a 1.00-cm cell. Where analyses are indicated only by symbols of the elements or functione, analytical results obtained for those elements or fmctions were within +0.4% of the theoretical valiies. Preparation of Compounds Listed in Table I. Method A . 2-Hydroxy-3-phenyl-4H-pyrazino[ 1,2-a]pyrimidin-4-one (I).--A mixture of 47.5 g (0.50 mole) of aminopyrazine and 118 g (0.50 mole) of diethyl phenylmalonate under S?was heated gradiially with an oil bath t o 160’. At this temperature an aspirator was attached and the system was evacuated and kept at approxiately 70 mm. After 2 hr at 160-170”, an additional 30 g of diethyl phenylmalonate was added and the mixtiire was kept a t 160-170” for 2 hr and the another 30-g portion of diethyl phenylmalonate was added and the heating was resumed for another 2 hr. The mixture was allowed to cool to ambient temperature, and the brown mass was crushed in a mortar with a pestle, triturated with ether, suction filtered, and recrystallized from glacial HOAc. Compound I is a high-melting (278” dec), yellow-gold solid insoluble in common organic solvents, except DAlF or DMSO. Its ir spectriim (Sujol) does not show O H stretch in the 3200-3600-cm-1 region but t,ather exhibits a hload absorption from 2300 to 3200 cm-1 with a maximiim at 3650 cm-1 that indicates intramolecular bonded OH or X H + . The carbonyl region has five peaks located at 1760, 1735, 1680, 1660, and 1600 cm-1. The IIV spectriim of the conjugate acid of I (spectrum obtained in 5 HySOa)exhibited Xmax a t 231, 267, 346, and 379 mp with e of 23.7, 8.78, 4.11, and 4.09, respectively. Even though I has ail extra ring N and a phenyl substit,uent its physical (high melting point, low solubility in nonpolar solvents) and spectral properties closely resemble those of “malonyl-a-aminopyridine.”l Both compounds have five peaks in the C=O region of the ir and four absorption maxima in the ultraviolet. As would be expected the ir peaks in the C=O region of I are each shifted to a higher frequency and the iiv maxima are shift,ed to a higher wavelengt,h. A pmr spectrum of I in ds-URlSOa showed the five phenyl protons as a complex multiplet centered a t 450 cps, ring proton at A \
