CORRELATION OF DIPEPTIDE AND TRIPEPTIDE DISTRIBUTION COEFFICIENTS WITH STRUCTURE VIA UNITARY MOLECULAR INDEXES

The unitary molecular structure indices, viz., the integrated molecula r transform (FTm), the integrated electronic transform (FTe), the inte grated charge transform (FTc), the normalized molecular moment (M-n), and the normalized electronic moment (M-e) were used in separate trial s to model the reported apparent distribution coefficients (log P') of 25 dipeptides and 34 tripeptides. Linear regressions indicated that t he two series should be considered separately as shown by the correlat ion coefficients and F statistics. In these cases, the former exceeded 0.75 generally and reached 0.795 for the FTe. The correlation coeffic ients for the FTc index were 0.692 and 0.380, respectively, for the tw o series and thus indicative of its inadequacy as a descriptor for thi s model. A bivariant regression of log P' against M-n and M-e did not improve on the monovariant models. The molecular weight as a structure surrogate gave adequate correlation coefficients but is not recommend ed as structure parameters are implicit rather than explicit. The M-n or M-e correlations may be used to estimate log P' for compounds simil ar to those in the dipeptide series, and FTe, likewise in the tripepti de series. The possible requirement for an amide group descriptor is d iscussed. (C) 1998 John Wiley & Sons, Inc.