120 



H. GOBIND KHORANA 



Chemical methods for the polymerization of mononucleotides would be of 

 similar value especially since they could add to the range of the polymers 

 available. Furthermore, in the deoxyribonucleotide field, polymers consist- 

 ing of one type of nucleotide have not been prepared enzymically as yet. 



a. Thymidine Oligonucleotides 



The reaction of thymidine-5'-phosphate with dicyclohexylcarbodiimide 

 or p-toluenesulfonyl chloride in anhydrous pyridine gives a mixture of 

 polymeric products. 18 The separation and isolation of pure components from 

 the mixture has been achieved by chromatography on cellulose anion ex- 

 changers often followed by preparative paper chromatography. 24 In the 

 main, two series of homologous oligonucleotides were obtained. 24 The first 

 are the linear oligonucleotides, the general structures of which are repre- 

 sented by (XXXIV). Thus, they contain the repeating naturally occurring 



O 



1 hymine 



OH 



(XXXIV) 



(XXXV) 



Thymine 



24 G. M. Tener, H. G. Khorana, R. Markham, and E. H. Pol, J. Am. Chem. Soc. 80, 

 6223 (1958). 



