Quantum molecular similarity. 3. QTMS descriptors

Building on the ideas of a previous paper [part 1, J. Phys. Chem. A 1999, 1 03, 2883] we present a new molecular similarity method based on the topolog y of the electron density. This method is directly applicable to QSARs and is called quantum topological molecular similarity (QTMS). It has been test ed for five sets of carboxylic systems including para- and meta-benzoic aci d, para-phenylacetic acid, 4-X-bicyclo[2.2.2]octane-1-carboxylic acids, and polysubstituted benzoic acids. in combination with the partial least squar es (PLS) procedure QTMS is able to produce excellent and statistically vali d regressions. It is shown that QTMS avoids certain challenges of tradition al Carbo-like similarity indices. Finally, QTMS is able to suggest a molecu lar fragment that contains the active center or the part of the molecule th at is responsible for the QSAR.