114 H. GOBIND KHORAXA 



(C6H 6 ) 3 COCH 2 / \ Thymine (C 6 H 6 )3COCH2/ \ Thyi 



OH O 



(XIII) / 



+ HO— P=0 



DCC / (1) OH 



' OCBy^ °\K (2)H + or 



II ^ \<r N H2 / pd 

 HO— POCH 2/ / U \ R 



OH |\| \/\ O 



O CH 3 C=0 



I 

 CH 3 C==0 



(XIV a), R = Thymine (XV a), R = Thymine 



(XIV b), R = JV-Acetyladenine (XV b), R = V-Acetyladenine 



(XIV c), R = A/-Acetylcytosine (XV c), R = iV-Acetylcytosine 



HOCH2/' \ Thymine 



OH 



(XVI a), R = Thymine 

 (XVI b), R = Adenine 

 (XVI c), R = Cytosine 



Scheme 2 



(XI Va) (Scheme 3). After removal of the protecting groups by successive 

 alkaline and acidic treatments, the desired product (XVIII) was obtained 

 in 68% yield. 



b. Thymidylyl-{3' — > 5')-deoxyadenylyl-{3' — * 5')-deoxycytidine (XIX) 20 



Analogously to the above synthesis, N ^'-O-diacetyldeoxyadenosine-S'- 

 phosphate was condensed with 5'-0-tritylthymidine and the product ob- 

 tained after alkaline treatment and purification (XVIIb) was made to re- 

 act with A7-3'-0-diacetyldeoxycytidine-5 '-phosphate (XIVc). The mixed 

 trinucleoside diphosphate (XIX) was obtained after removal of the pro- 

 tecting groups. 



The synthesis of mixed and higher oligonucleotides is certainly feasible 

 and the next few years should see progress in this field. The major problems 

 to be overcome are (1) insolubility in anhydrous organic solvents (2) separa- 



