Object of the present invention is to develop an artificial synthesis system of various peptides having an azole derivative structure and develop a library of such peptides. The present invention provides a method of producing a peptide having, in the backbone thereof, an azole derivative structure comprising the step of: synthesizing a substrate peptide of an azoline structure introducing enzyme having, in the modified region thereof, at least any one of the following amino acids, ##STR00001##
[in any of the compounds, X.sub.1 represents a group selected from the group consisting of SH, OH, NH.sub.2, SR.sup.1, OR.sup.1, NHR.sup.1, and N.sub.3 (R.sup.1 represents a protecting group), X.sub.2 represents an easily eliminable group; and X.sub.3 represents hydrogen or a substituted or unsubstituted alkyl or aryl group having from 1 to 10 carbon atoms]; reacting the substrate peptide with an azoline structure introducing enzyme to obtain a peptide having an azoline derivative structure; and converting the azoline derivative structure of the resulting peptide into an azole derivative structure by inducing an HX.sub.2 elimination reaction of X.sub.2 group.

Object of the present invention is to develop an artificial synthesis system of various peptides having an azole derivative structure and develop a library of such peptides. The present invention provides a method of producing a peptide having, in the backbone thereof, an azole derivative structure comprising the step of: synthesizing a substrate peptide of an azoline structure introducing enzyme having, in the modified region thereof, at least any one of the following amino acids,

##STR00001##

[in any of the compounds, X.sub.1 represents a group selected from the group consisting of SH, OH, NH.sub.2, SR.sup.1, OR.sup.1, NHR.sup.1, and N.sub.3 (R.sup.1 represents a protecting group), X.sub.2 represents an easily eliminable group; and X.sub.3 represents hydrogen or a substituted or unsubstituted alkyl or aryl group having from 1 to 10 carbon atoms]; reacting the substrate peptide with an azoline structure introducing enzyme to obtain a peptide having an azoline derivative structure; and converting the azoline derivative structure of the resulting peptide into an azole derivative structure by inducing an HX.sub.2 elimination reaction of X.sub.2 group.