Simple averaging procedure for aromatic ring system: mean molecular fragment of tryptophan metabolites

A simple averaging procedure of bond lengths and angles applicable to an aromatic ring system was applied to the crystal structures of the tryptophan metabolites analyzed so far, as an example. Statistical analysis showed no marked effect of the 5-substituent on the molecular dimensions of the 3-substituted indole ring in tryptophan metabolites. The standard bond lengths and angles of the 3-substituted indole ring were calculated according to the statistical averaging procedure outlined here and using data from 35 tryptophan metabolites; the interatomic correlations of the indole ring have been discussed based on these values. The result suggests the validity of the D² statistic for averaging the planar ring structure in aromatic systems.