Synthesis of 3-3-gem – di – C –Nitromethyl Nucleoside Analogues of Possible Biological Activity

Synthesis of new nucleoside analogues of the type : 3  , 3 gem – di – C – nitromethly , expected to have useful application in the chemotherapeutic treatment of AIDS , cancer and microbial infections. The synthesis involved the condensation of the appropriate sugar derivative ( i.e . 3 , 3  – gem – di – C – nitromethly – 1– ribofuranose ) with nitrogen bases , such as , uracil and theophllin following a multi step scheme starting from diacetone golucose (1) (scheme 1) .The prepared compound were identified by spectroscopic methods ; ir , mass , H and C nmr. ةصلاخلا ضحت ي عون نم ةديدج ديسويلكوين تلاثامم ر 3 , 3 يئاانث مئاو تلا – C – ة يـئاميكلا ةـج لاعملا ي فـ اـهنم ةدافتـسلاا لـمتحم ل يـثمورتين ) chemotherapy ( ة يموثرج لا ضارملالو ن اطرسلاو ةعانملا صقن ضارملا . يركسلا ءزجلا تاقتشم فيثكت ريضحتلا نمضت 3 , 3 انث مءوتلا يئ – C – ليثمورتين – D – لثم ةينيجورتن دع اوق عم زونارويف زوكولك نوتيسا يئانث نم أدبي تاوطخلا ددعتم راسم عابتاب نيلفو يثلاو ليسراو يلا ) 1 ) ( ططخملا 1 . ( توربلا ىسيطانغملا يوونلا نينر لاو  ة لتك لاو  ءارمح لا تحت ةعشلاا ةيفيط لا قرطلا ةطساوب ةرضحملا تابكرملا صيخشت مت ريظنو ينو نوبراكلا 13 .


INTRODUCTION
The 2 , 3didexy nucleosides have shown importance in several established chemotherapies (anticancer , antiviral and antibacterial ) and other attractive field like immunomodulation or regulation of gene expression which may constitute new therapeutic approaches (1,3) . The board application of modified nucleosides especially in the inhibition of the human immunodeficiency virus (HIV) (4,5) , have targeted the investigation for utilizing new nucleoside analogues .Efforts have primarily focused on modification of the carbohydrate portion of the natural nucleosides because cellular kinases are more tolerant of these changes than changes within the base moiety (6) . These observations , have led us to commet the synthesis of a variety of nucleoside analogues contaning 3 , 3 -gem di -Cnitromethyl substituent at the sugar portion .

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3g, 22.9 mmol ) was dissolved in methanol and IN H 2 SO 4 (30ml) was added . The reaction mixture was left to stand at room temperature for 3hr .The resulting mixture was then neutralized by adding solid sodium hydrogen carbonate and then extracted with chloroform .The chloroform extract was dried over anhydrous sodium sulphate and gave upon evaporation the diol (6) as a syrup (6.0g , 80.4%).IR(smear)v(3450)cm -1 (OH) .

-Deoxy
The diol (6) (2g ,6.2mmol ) was dissolved in ethanol (40ml) and wellstirred , then saturated solution of sodium hydrogen carbonate (2ml) was added followed by a solution of sodium metaperiodate ( 1.32g ,6.2 mmol ) in 70 ml w ater the resulting reaction mixture was stirred 3hr after which the excess sodium metaaperidate was destroyed by adding few drops of ethylene glycol .The resulting aldehydo sugar was immediately reduced with sodium borohydride (012g).After the reaction mixture was kept with stirring for 4 hr ,acetone (0.5ml) was added and the mixture was further stirred for 30 minutes . The solid residue was removed by filtration and the filtrate was extracted with methylene chloride , dried over anhydrous sodium sulphate the solvent was removed to give (7) as a syrup (1.39g, 76.8%).IR (smear )v(3450)cm -1 (OH). 1 (7) (2.4g , 8.2 mmol ) was dissolved in anhydrous pyridine (6.7ml ,83 mmol ) after external cooling with ice , benzoyl chloride (0.96ml ; 8.3mmol )was added dropw ise . The reaction mixture was kept at room temperature for 24 hr then iced water was added .The resulting syrup was extracted with petroleum ether (b.p. 40 -60 C ) ,then dried with anhydrous sodium sulphate , filtered and concentrated under reduced pressure . Traces of pyridrne were remove by coevaporation with dry toluene .The benzoate derivative (8)

1,2 -Di
The acetylated sugar (9) (1g,2.2 mmol) was treated with 50%(W/V) hydrogen bromide in acetic (3ml) the solution was kept at 0C for one hour then poured in to an ice cooled dichloromethane (50ml ) , washed with iced water , and then with saturated aqueous solution of sodium bicarbonate to remove the remaining acid .After a final wash with iced water , the dichloromethane layer was dried over anhydrous sodium sulphate and the solvent was removed to give (11) as syrup (0.9g , 95%). The isolated sugar bromide (11) was used directly for the nucleoside synthesis .

Synthesis of theophylime nucleoside analogue
The theophylline mercury salt (10) (0.55 g , 0.98mmol ) was finely pow dered , suspended in (150ml )sodiumdried xylene and the solvent was partially distilled to remove traces of water azeotropically .When the temperature of mixture was raised to 137 C , the residual suspension was allowed to cool (below 50 C ) . The acetylated sugar bromide (11) (0.9gm , 1.96mmol )in xlyene was then added and the reaction mixture refluxed with vigorous stirring for 15 minute . The xlyene layer was washed with 20% aqueous potassium iodide to remove the remaining traces of the mercuric salt , washed with water , dried over anhydrous sodium sulphate and the solvent was removed to give after silica gel column chromatography with chloroform as an eluent the acetylated nucleoside (12) (0.57g,52%Jas syrup .IR (smear ) v (2850 -2950 )cm -1 (C -H ) .

Synthesis of protected uracil nucleoside analogue
The acetylated sugar (9) (0.44g, 1mmol ) and silylated uracil (13) (0.29 g ,1.1mmol ) were dissolved in anhydrous 1,2dichloroethane (10ml ) . Anhydrous stannic chloride (0.08ml , 0.684 mmol ) w as then added in the presence of few pellets of molecular sieve 4A and reaction mixture was stirred at 23 C , tIc (chloroform -mcthanol )9:1) show ed the reaction was complete after 16 hrs . The reaction was then poured on an exess sodium bicarbonate solution and extracted with methylene chloride .The combined methylene chloride extracts was dried over anhydrous sodium sulphate , and the solvent was removed to give (14) (0.6 g , 40,3%),IR (smear )v(2850 -2950 )cm -1 (C -H ),(3350)cm -1 (N -H ). The product was purified on silica gel column using chloroform as eluent .Two different fractions were isolated , the first one (14) (0.018g) as white semisolid which represented The silyated nucleoside . 1 (5) was obtained from Dglucose according to the method reported earlier by one of us (7) . Selective hydrolysis of the 5,6isopiopylidene group of the 3,3gem -di-Cnitromethyl --Dribohexofuranose (5) with in sulphuric acid in methanol (8) gave the monoisoropylidene derivative (6) as a syrup in 80.4% yield .Oxidation of the diol (6) with sodium periodate effected the cleavage of C 5 -C 6 Bond and resulting intermediate aldehyde derivative was reduced immediately with sodium borohydride to give the 3deoxy (8) . The primary 5 -OH group in (7) was then protected by convcrsion to the 5benzoate ester (8) . Treatment of (7) with benzoyl chloride in pyridine (9) .overnight gave the 5 - (8) as syrup in 50% yield . The final step in the synthesis of the protected sugar moiety before carrying out the coupling reaction with nucleobases , was the removal of 5 -O -1,2acetal of 5 -Obenzoyl derivative (8) with 99% trifluoroacetic acid followed by acetylation .Acetylation of the 1and 2hydroxyl groups was performed with acetic anhydride in pyridine (9) (9) as a syrup in 90% yield .
The sugar bromide (11) was condensed with bis (theophylline -7yl )mercury (10) as the activated base in anhydrous xylene under reflex which afforded the desired theophylline nucleoside analogue (12) , after silica column chromatography , as a syrup in 52% yield .The theophylline (1,3dimethylxanthine )base has been used because of its availability and due to the fact that only one of its nitrogen atom (N -7 ) is reactive , therefore mixture of different nucleoside analogues may be avoided . The reaction of theophylline w ith mercuric chloride in aqueous alkali afforded the mercury derivative rather than the chloromercury one , and it was assigned that N -7 was the predominate position of attachment of mercury group in the theophylline . It has also been demonstrated that the mercury derivative of theophylline couple with acylglycosyl halides at N -7 (12 -14) and involves direct displacement of the mercury group from nitrogen by the incoming acylgycosyl halide (11) . For the synthesis of 1 - (14), the modified Hilbert -Johnson procedure using simply Friedel -Crafts catalysts like SnCl 4 was followed (15) . The 1,2di -Oaceylribofuranose derivative (9) was coupled with the silylated uracil (13) in 1,2dichoroethane in the presence of anhydrous stannic chloride as Lewis acid .The reaction involved the conversion of the protected sugar (9) in to the reactive electrophilic 1,2acetyloxonium ion followed by the silylated uracil (13) attak to afford the protected uracil nucleoside analogue (14) with the regeneration of the catalyst . The formation of 1,2acetyloxonium ion determined the exclusive formation of the -anomer (14) (15 -16) , which was separated as white semisolid and characterized by its 1 H NMR spectrum . Another fraction (14a) w as separated on the silica gel column and identified from its 1 H NMR spectrum as being the desilylated nucleoside (14a) .