[Combined use of bucolome and pyrazolone derivatives (II). Complex formation due to interaction between bucolome and pyrazolones].

We have already reported that bucolome (BCP), a non-steroidal anti-inflammatory agent, potentiates significantly the analgesic and antipyretic effects of pyrazolones which are substituted by alkylamino group at 4-position of the pyrazolone ring. Physical and quantum chemistry were applied to the mechanism of this synergistic action. The solubility of BCP was markedly increased in proportion to elevation of aminopyrine (AM) concentration, but not by a combination with isopropylantipyrine (IP). The binding of BCP to bovine serum albumin was slightly inhibited by AM, but not by IP. The mixture of AM and BCP in aqueous media generated optical absorption in the ultraviolet differential spectrum, due to the charge transfer interaction. The results of the infrared or NMR spectrum demonstrated the formation of a hydrogen binding in non-aqueous media between BCP and AM. From the calculation of the charge on an atom, the energy of the highest occupied molecular orbital and the frontier electron density, BCP is considered to be a good electron acceptor. The beta-units of Mho of pyrazolones were found to correlate with the potentiation coefficient of analgesic activity in combination drugs. These results suggest that the complex formation between BCP and pyrazolones is an important factor for the synergism of action and is due to the charge transfer interaction and the hydrogen binding of both molecules.