Use of RP-TLC for Determination of log Pof Isomeric Chalcones and Cyclic Chalcone Analogues

log P values of 29 biologically active chalcone (1) and cyclic chalcone analogues E-2-(X-benzylidene)-l-indanones (2) and E-2-(X-benzylidene)-1-tetralones (3) have been determined by an optimized and validated RP-TLC method. RP-TLC was performed on silanized silica gel 60F254 as stationary phase with methanol-water, 60 + 40 (v/v) as mobile phase. The RP-TLC method was validated by analysis of three drugs, diazepam, progesterone, and PGE1 ethyl ester, with known log PSF (shake-flask) values. The experimentally determined log PTLC values were compared with the log P values predicted by use of the CLOGP program. On the basis of the log PTLC values of the investigated chalcones (1), the cyclic chalcone analogues (2, 3), and previously investigated, related, E-2-(X-ben-zylidene)-1-benzosuberones (4) the effect on lipophilicity of ring size and the nature and position of substituents were studied. It was found that the open-chain chalcones (1) and the five-membered ring E-2-(X-benzylidene)-1-indanones (2) have similar lipophilicity. Changing the ring size from five to six (3) and from six (3) to seven (7) resulted in the expected increase of the log P values of the compounds. The results indicate importance of steric and electronic factors in the lipophilicity of the compounds investigated.