748 Journal of Medicinal Chemistry, 1971, Vol, 14, iVo. S
CHHI,D.\A
~ Iloxc: D
Synthesis of Naturally Occurring 6-Ureidopurines and Their Nucleosides] GIRISHB. CHHEDA*A K D CHUKGIL HONG General Clinical Research Center, Roswell Park Memorial Institute, Buffalo, S e w I'ork
14203
Received *Youember 3, 19'70 The naturally occurring modified purines, AV-(purin-6-ylcarbamoyl)threonine (PCT, I ) and S-(purin-B-ylcarbamoy1)glycine (PCG, IV), and their ribosides, PCTR (11) and PCGR (111),have been synthe&ed. Facile syntheses of the key intermediates, ethyl purine-6-carbamate ( V I ) and its riboside (XI), were achieved by new methods. Displacement of the E t 0 group of urethane3 VI and X I with L-threonine and glycine gave PCT (I), P C T R (11),PCG (IV),and PCGR (111). Compounds I and I1 were also prepared through reaction of 2',3',5'tri-0-acetyladenosine with a suitably blocked threonine isocyanate, followed by deblocking. These cyuthetic studies confirm the earlier suggestion that the threonine of natural compound I hay the L configuration.
A novel modified purine in which an amino acid, threonine, is attached to the SH, of adenine through a ureidocarbonyl group, has recently been isolated and characterized.2a Structurally, it was shown to be N-(p~rin-6-ylcarbamoyl)threonine~~ (PCT, I, Scheme I). This ureidopurine is of general occurrence in
H
m,PCG,R.-CHzCOOH
~HOH
A
c AcO
O
d OAc
A
c
O
d
ACO
OAC
ACO
OAC
H
O
d
.VI, PCGR, R r -CH2COOH CH3
HO OH
zuc
=
tRNL42cof yeast, Escherichia
c o l i , 2 a tobacco tissue,*d and the human spleensze Its riboside, N - [(S-p-D-ribofuranosyl-9H-purin-6-yl)carbamoyl]threonine (PCTR,
(1) This study was presented by C . I . Hong, G. B . Chheda, and S. P. D u t t a , 160th National Meeting of t h e American Chemical Society, Chicago, Ill., Sept 1970, Abstract No. M E D I 55. This study was supported b y National Science Foundation Grant G B 8690 and U. S.Public Health Service Grants 1-Mol-FR00262-05, CA 10835, and G R S FR05648-04. (2) (a) G . B. Chheda, R . H . Hall, D . I. Magrath, J. hlozejko, .\I. P . Schweizer, L. Stasiuk, and P. R. Taylor, Biochemistry, 8, 3278 (1969) ; (bj M . P. Schweizer, G . B. Chheda, R . H . Hall, and L. Baczynskyj, ihid., 8, 3283 (1969). (c) Abbreviations used are as follows: P C T R , N-[g-(@-D-ribofuranosyl-9H-purin-6-yl)carbamoyl]threonine; P C T , K-(purin-6-ylcarhamoyllthreonine; TAA, 2',3',5'-tri-O-acetyladenosine; (d) JT. H . Dyson, C . & Chen, 'I. S.X . h l a m , R . H. Hall, C. I. Hong, and G. B . Chheda, Science, 170, 328 (1970); ( e ) A . hlittelman and G. B. Chheda, 10th International Cancer Congress, Houston, Texas, M a y 1970, Abstracts, p 386.
11), has been identified in hunian and rat Sequence determination of tRSAI1" by Taliemura 2nd coworkers4 revealed that 1'CTR occupied :i position adjacent t o an anticodon, I-Li-C. Ishilrura, et ul.,; have recently reported that I'CTIt ic alio preient :tt the same anticodon adjacent position iii 1 oiiyl, and seryl tRKXs which respond t o codons. Despite lrnonledge of its unique location i l l several specie5 of t R X a the exact function of thii threonine-containing nucleoside still remain. unknon 1 1 Recently, Schweizer, et d 1 6 a have isolated ;I glycititlcontaining ureido nucleoside, il'-(puriii-6-ylearb~~nio! 1)glycine riboside (PCGR, 111), from yeast t R S A I n order to make available sufficient quantities of thi. class of compounds for pharnmcological and biochemical studies arid for the structure proof of the n:itur:tl compounds, this synthetic work n as undertaketi. The present paper describes the synthetic methods and chemical properties of I'CT (I), PCG (IV), :tnd their nucleosides, PCTR (11) and I'CGR6b (111). 'i'ht~ acylation of adenine by eth! 1 chloruforniiite \\;I\ a l ~ o fully investigated, and a one-step s!-nthe,is of 1 lie required key intermediates, ethyl puriiie-6-carb:ii~i:~t~ (VI) arid its riboaide, has been achieved. Initially, thiz urethane VI \\a. prepured i n 4 \tcps starting from G-trichloronieth!lpurirle (V), :iceording to the method of Ginrr-Sorrolln :tiid I3endich.'* Tht. modifications in the conver4on of 6-trichlorom purine (V) to purine-G-carboxnniide rezulted ill :in yield, as compared nit11 t h r reported >ieltl of 3 I n spite of improvementi in the !ields to ric:u.l~ (111:t~ititative in each ,tep,'a this procedure for priyxirig the urethane T'I, still proved t o be ver) laboriom : ~ u d expensive, thus necessitating :t search for :I mor(' direct method of synthesih. For this purpo%e,the reaction of adenine nith ethyl chloroformate n a s itudied under various conditioIi..' ,') Equimolar aniouiits of adenine and Et02CC1 in pyridine at 33" for 3 hr gave a modest yield of ethyl 6-aminopurine-9-carboxylate (VIII). With :i threefold ( 3 ) (a) G. U. Chheda, Life Sci.. 8, 979 ( 1 9 0 9 ) ; (b) 6 . 1 3 . L'iil~eda, 1 1 , X i g h t , A. Mittelman, and > I , P.Sclliveizer, 15Rt11 Xational 1Ieeting of tile American Chemical Society, S e n T o r k , 'i.T., Gept 190!1, . \ h t r n c t S I > M E D I 70. (4) S. Takemura, hI. IIurakami, and 11. nliyazaki, .I. B i o r i ' r v i I 'l'okii") 66, 5.53 (1969). (5) H.Ishikura, >-, Yamada, I C=N): nnir 6 l..X (d, 3, J = 6 I&, !iO ((: -(:, i i n i i ' 6 1..X ((1, :;, J .= 0 l l z , L'1i7i, ,-!.(I &:; (111, - l i j 4'-Il>.i'-fi),0 . 4 h (,ti, 1, J =- .i.5 I I L , 1 ' - I I ;
