May 1907
475
Some Biologically Active N6-Methylated Adenosine Analogs
CHARTI RNCHi
'*
(I) condensation
G. GOUGHA N D AI. HELEN~ I A G U I R E
(ii) methanohc hH3
HgCl
Smith Kline and French Institute, Department of Pharmacology, University of Sydney, Sydney, Australia
Received September 20, 1966 Revised Manuscript Received November 21, 1966
2a, R d.
R
elk
Several 2-substituted adenosines have been shown to possess vasodepressor properties of greater duration of action and of greater potency than those of adenoand to inhibit the adenosine diphosphate mediated agglutination of blood platelets in vivo and in vitro.31~ 2-Chloroadenosine is the most potent of these analogs and would appear to be of potential therapeutic value in the treatment of hypertension or of thrombosis, except for the concomitant toxic effects it has on the mammalian heart. This analog has been shown to cause heart block in the guinea pig2and in man.5 As a first approach to structural alteration which may give analogs having the beneficial vasodilatatory effects of 2-substituted adenosines without their concomitant toxic heart effects, the N6-mononiethylated derivatives of five 2-substituted adenosines, 2-chloro-, 2-methylthio-, 2-methoxy-, 2-ethylthio-, and 2-trifluoromethyladenosines (la-e), were synthesized, together with 2-chloro-N6-dimethyladenosine (If).
f, R
The analogs (la and d-f) were prepared by Davoll's modification6 of the classic Fischer-Helferich purine nucleoside synthesis' (Chart I). The appropriate 2substituted 6-methylaminopurines were converted to their chloromercuri salts (2) and these were condensed with 2,3,5-tri-O-benzoyl-~-ribosyl chloride (3). Removal of the benzoyl blocking groups with methanolic ammonia gave the required nucleosides. (1) D. A. Clarke, J. Davoll, F. S. Philips, and G. B. Brown, J . Pharmacol. E'zptl. Therap.. 106, 291 (1952). (2) R. H. Thorp a n d L. B. Cobbin, Arch. Intern. Pharmacodyn., 117, 95 (1959). (3) G. V. R. Born, A. J. Honour, and J. R. A. Mitchell, Kature, 902, 761 (1964). (4) G. V. R. Born, ibid., 202, 95 (1964). ( 5 ) R. H. Thorp, private communication. (6) J . Davoll and D. A. Lowy, J . A m . Chem. Soc., 78, 1650 (1951) (7) E. Fisciier and U. Helfericli, Chem. Ber., 47, 210 (1914).
RzO ORA
= H ; R1 = C1 3, = H: Rt SGH; ._ _ - ~ " = H f R; = CF3 = CHs; = C1
R2 = COCsH5
RI
la and d-f
f2-Chloro-N6-methyladenosine (la) was also obtained via the fusion method8 (Chart 11). 1-0-Acetgl-2,3,5tri-0-benzoyl-p-D-ribofuranose ( 5 ) was fused with 2,6dichloropurine (4a) in the presence of p-toluenesulfonic acid to give the blocked 2,6-dichloropurineribosidega which was siniultaneously deblocked and niethylaminated by treatment with anhydrous methylamine in methanol at room temperature. By this method la was obtained in 42y0yield. CHARTI1
7'
R,nrw
OCOCH, (i) fusion + (ii) methanolic CH ; N H ?
n
4a, R1 = C1 b, R1 SCHI
e ; R = H : R 1 = CF3 f, R = CHI; RI = C1
%
RiO OR, 5,
Rz
= COCdIj
l a and b
The fusion mlethod was also used for the preparation of 2-methylthio-A"j-methyladenosine(1b),lo starting with 2-niethylthio-6-chloropurine (4b). It has been reportedsb that fusion of 4b with tetra-0-acetyl-P-Dribofuranose in the presence of p-toluenesulfonic acid, followed by treatment of t'he blocked intermediate with niethanolic ammonia gave a 36% yield of 9-p-D-ribofurariosyl-2-niethylthio-6-chloropurine. I n our hands fusion of 4b with either 5 or tetra-O-acetyl-p-D-ribofuranose in the presence of p-toluenesulfonic acid, followed by prolonged treatment at room temperature of the intermediate blocked nucleoside with methanol saturated with methylamine gave only a poor yield of
lb. (8) For the acid-catalyzed fusion reaction of purines with tetra-0-acyl-Dribofuranose t o give @-nucleosides see (a) T. Pato, T . Simadate, and 1.. Ishido, r V i p p o n Kagaku Zasshi, 81, 1440 (1960): (b) T. Siinadate, Y. Ishido, and T. Sato, i b i d . , 82, 938 (1961); (c) G. Gough and AI. H . hlapuire. J . JJed. Chem., 8, 866 (1965). (9) (a) I n subsequent work ire found t h a t complete reaction of 2,6-dichloropurine with l-0-acetyl-2,3,5-tri-0-benzoyl-p-~-ribofuranose was achieved without a catalyst simply by fusion f o r 45 min in uacua a t 13C-140°. (b) Fusion of acetylated 2-methylthio-6-chloropurine witti I-O-acetyl-2,3,5-tri-Obenzoyl-p-D-ribofuranose without a catalyst gave a clear melt a t 16O", b u t there was no reaction. T h e attempted fusion of 2-methylthio-6-chloropurine with t h e sugar without a catalyst a t 185-195O resulted only in considerable decomposition. T h e reactivity of other 2-substituted 6-chloropurines in the fusion reaction with a n d without a catalyst is presently being investigated. (10) M. Ikehara. T. Ueda, S. Horikawa, and A. Yamazaki, Chem. Pharm. Bull. (Tokyo), 10, 665 (19621, reported t h a t reaction of N e K H ? with 2,6-dimethylthio-9-(2,3,5-tri-O-benzoyl)-@-~-rihofi1ranos)-lpurine gave lb, which was isolated a s a picrate salt. Spectral data only uerc reiiorted. p : , X HCI 271 Inp, A!,O&V S r O l i L i Y , 239 lnp. I
-
r .
1 h r c o~f tlic ;iii:ilogh, l a , l b . aiicl l e IMVC becii +lio\vii to be potent inhibitors of cardiac aderiosine deaminase, more potent than their corresponding nonmethylated aiidogs, 'I-chloroaclrrioiiiie. '2-nicthvIthioadenoRirle. aiid
KOTES
May 1967
477
pH 13
Dern a t i l e of adenosine
PH 1
2-Chloro-S6-methyl2-Chloro-S6-dimethyl2->Iethylthio-S6-methyl2-E t hy1thio-*Yfi-met hyl2-Trifluoronieth? l-S6-methy1( + 0.3H20) 2-lIethoxy--\ 6-methyl- ( + I L O )
270(15 5 ) 278(18 7 ) 272(15 8) 272 5 ( 1 7 1) 266(13 0 )
268 ( 1 6 . 8 ) 276 (19.6) 279 (15,9),239 (19.8) 280 (17.2) 240.5 (21.3) 265 (13.4)
-53.5+0.2(0.3355) -58.6f.OO.2(0.2937) -40.2 i 0.2(0.9877) -34.6 + 0 . 2 ( 1 . 0 3 2 ) -48.8&0.2(0.9685)
2 i 6 . 5 ( 1 4 1)
260 (16.2)
-46.6
of HgC1, (10.86 g, 40 mmoles) in ethanol (350 ml). A gel-like suspension of the chloromercuri derivative gradually formed; the pH was adjusted to 8 with aqueous NaOH, and the suspension was kept at, room temperature for 12 hr. The product was filtered, washed with water and ethanol, and dried in cacuo. The material (29.9 g, 94'3) was added to anhydrous xylene (600 ml) and further dried by azeotroping iinder a Deaii-Stark head. A xyleiie (50 ml) sollition of 3,'* which was prepared from 20.16 g (40 mmoles) of 5,19 was added and the mixture was refliixed and stirred for 3 hr. The hot suspension was filtered and the filtrate was evaporated leaving an oil which was dissolved in CHC13 (100 ml). The filter cake was washed with three 100-ml portions of hot CHCL. The chloroform solutions were combined and extracted with two 100-ml portions of 30% aqueous KI and two 100-ml portions of water and dried (Ya2SO4j. Chloroform was evaporated leaving a viscous orange oil, which was kept for 2 days a t 2' with absolute methanol (100 ml) saturated with XH3. The oil gradually dissolved. l\Iet,hanol was evaporated leaving a brown oil (10.0 gj. This was partitioned between water ( 5 0 ml) and CHC13 (50 ml.). The aqueous extract was extracted once more (CHC13) and evaporated to a clear brownish glass, which crystallized when t,riturated with ethanol. Filt,ration yielded 6.1 g of brown crystals, and two recrystallizat,ions from methanol gave 4.3 g (34%) of la. Two more recrystallizations from methanol gave pure la, mp 203-204". The spectral data are recorded in Table 11. Anal. Calcd for CllH14ClSj04: C, 41.84; H, 4.47; N, 22.19. Found: C, 41.88; H, 4.82: N, 21.83. (ii).-A mixture of 2,6-di~hloropurine~~ (18.9 g, 0.1 mole) and 5 (50.4 g, 0.1 mole) was heated in vacuo at, 135' in a rotating flask until a clear melt was obtained. Considerable evolution of acetic acid occiirred at this stage. The reaction flask was cooled to room temperature, anhydrous p-toluenesulfonic acid (200 mg) was added, and the flask again was heated in vacuo with rotation a t 140" for 25 min. A vigorous gas evolution occurred and a clear glass was obtained. The flask was cooled to room temperature and the product was dissolved in CHCl, (500 ml). The chloroform solution was washed with three 200-ml portions of saturated aqueous NaHCOa and with two 100-ml portions of water, filtered, and dried (N2S04). Evaporation of CHC1, left a clear pale yellow glass which was triturated with hexane to give the blocked 2,6-dichloropurineriboside as a hexaneinsoluble cream powder (60 g). Thin layer chromatography on silica gel in CHCl3-ethyl acetate ( 9 : 1) showed that, the blocked nucleoside was essentially homogeneous, and it was not further purified. Five grams of this product was treated with 300 ml of anhydrous methanol, and the mixture was saturated with anhydrous methylamine at 0". It was kept a t 3' for 3 days and the solid gradually dissolved. The solution was then transferred to an autoclave and kept for 2 days at, room t,emperature. l l e t h anol was evaporated leaving a clear brown glass which was dissolved in water (50 ml). The aqueous solution was extracted with three 20-ml portions of CHCl, and evaporated to a viscous brown oil. Triturat~ion of this with methanol gave brownish crystals (1.34 g ) which were recrystallized from ethanol to give 1.1 g of Is, mp 205-207". A mixture melting point with the product obtained by route i and comparison of the spectral properties of the two products showed them to be identical. 2-Methylthio-S6-methyladenosine (Ib). (i).-2-Methylthio6-chloropurinez1 (2.0 g, 9.9 mmoles) was heated in uacuo with 5.04 g (10 mmoles) of 5 to 140' without appreciable solution of (18) H. RI. Kissman, C . Pidacks, and I3. R. Baker, J . A m . Chem. Soc.. 7 7 , 18 (1955). ( 1 Y ) E. F. Recondo a n d H. Rinderknecht, Hela. C h i m . Acta, 42, l l i l (1959). (20) .i. G . 13eaman a n d R. IC. Robins, J . A p p l . Chem., 12, 432 (1962). (21) C. \\-. h'oell a n d R . I
