THE NUCLEOPROTEIDS. 281 



Very closely related to this group of nucleic acid cleavage-products are 

 other compounds, which, instead of having a purine ring, contain one of 



pyrimidine : 



(1) N = CH (6) 



(2) HC CH (5) 



II II 



(3) N CH (4) 

 Pyrimidine 



The syntheses of the members of this series and their constitution indi- 

 cate their close relation to the purine derivatives. We are mainly indebted 

 to A. Kossel for their discovery. Ascoli 1 first found uracyl in yeast- 

 nucleic acid. It has the following constitution: 



NH CO 



CO CH 



.1 II 

 NH CH 



Uracyl = 

 2, 6-dioxypyrimidine 



Emil Fischer and Georg Roeder 2 succeeded in synthesizing it. These 

 same authors also established the constitution of another pyrimidine base, 

 thy mine. It is a 5-methyluracyl, 



NH CO 



O C . CH 3 



I II 

 NH CH 



Thymine = 

 5-methyluracyl (5-methyl-2, 6-dioxypyrimidine) 



This compound was first isolated from thymus nucleic acid by A. Kossel 

 and Neumann. 3 



Finally, we are acquainted with a third pyrimidine derivative, cytosine, 

 which was also separated from thymus nucleic acid by Kossel and 

 Neumann. 4 It has been synthetically prepared by Wheeler and Johnson, 5 



1 A. Ascoli: Z. physiol. Chem. 31, 161 (1900-01). A. Kossel and H. Steudel: ibid. 

 37, 245 (1902). 



2 E. Fischer and G. Roeder: Ber. 34, 3752 (1901). 



3 A. Kossel and A. Neumann: ibid. 26, 2753 (1893); Z. physiol. Chem. 22, 188 (1896). 

 H. Steudel and A. Kossel: ibid. 29, 303 (1900). H. Steudel: ibid. 30, 539 (1900); 32, 

 241 (1901). W. Jones: ibid. 29, 20 (1899); 30, 461 (1900). W. Gulewitsch: ibid. 27, 

 292 (1899); 27, 368 (1899). O. Gerngross: Ber. 38, 3408 (1905). 



4 A. Kossel and A. Neumann: Ber. 27, 2215 (1894). A. Kossel and H. Steudel: 

 Z. physiol. Chem. 37, 177 (1902); 37, 377 (1903); 38, 49 (1903). 



5 H. L. Wheeler and T. B. Johnson: Am. Chem. J. 29, 492 and 505 (1903). 



