29580
A novel series of pyrido [ 2 , 3 - d ] pyrimidines as selective and potent DHFR inhibitors against these opportunistic infections are presented .
 Chemical: pyrido [ 2 , 3 - d ] pyrimidines
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: pyrido [ 2 , 3 - d ] pyrimidines