17817
Improvement of the inhibitory activity and chemical stability of this series of compounds was respectively achieved by the introduction of bulky groups at the 4 - position and 1 - position of the piperidinyl glycine , leading to a series of potent and stable DPP - IV inhibitors .
 Chemical: piperidinyl glycine
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: piperidinyl glycine