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The interaction of isopenicillin N synthase with homologated substrate analogues delta - ( L - alpha - aminoadipoyl ) - L - homocysteinyl - D - Xaa characterised by protein crystallography .
 isopenicillin N, delta - ( L - alpha - aminoadipoyl ) - L - homocysteinyl - D - Xaa
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 isopenicillin N, delta - ( L - alpha - aminoadipoyl ) - L - homocysteinyl - D - Xaa