17416
{ [ ( 2 - [ ( Guanine - 9H - yl ) methyl ] propane - 1 , 3 - diyl ) bis ( oxy ) ] bis ( methylene ) } diphosphonic acid ( compound 17 ) exhibited a Ki value of 30 nM for human HGPRT and 70 nM for Pf HGXPRT .
 Chemical: { [ ( 2 - [ ( Guanine - 9H - yl ) methyl ] propane - 1 , 3 - diyl ) bis ( oxy ) ] bis ( methylene ) } diphosphonic acid
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
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Answer:
 Chemical: { [ ( 2 - [ ( Guanine - 9H - yl ) methyl ] propane - 1 , 3 - diyl ) bis ( oxy ) ] bis ( methylene ) } diphosphonic acid