1419
The docking results also showed that the formation of new H - bonds between the N - H of the ethylenediamine group linked to the 6 - alkoxy site and Asp776 / Cys773 in the binding pocket of EGFR makes compounds 19 ( IC50 = 12 . 1 +/- 1 . 6 nM ) and 20 ( IC50 = 13 . 6 +/- 0 . 8 nM ) the most potent EGFR inhibitors in this class and worthy of further modification to obtain more potent anticancer compounds .
 Chemical: H; Chemical: N - H; Chemical: ethylenediamine; Chemical: 6 - alkoxy; Chemical: Asp776; Chemical: Cys773
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: H; Chemical: N - H; Chemical: ethylenediamine; Chemical: 6 - alkoxy; Chemical: Asp776; Chemical: Cys773