Abstract :
Two muscular relaxants (MR), methyl ethers of N-benzoyl tyramine (Riparin I) and N-(1,6-dihydroxybenzoyl) tyramine (Riparin III) were
studied with X-ray diffraction (XRD), optical spectroscopy and semi-empirical calculations. The XRD data show that the CaO group in
Riparin I is 348 out of plane from the closest benzene ring. The abinitio calculations using RHF/6-31G* suggest that the dihydroxybenzoyl
(DHB) group in Riparin III forms intramolecular hydrogen bond between the H of the O–H group and the O of the CaO group, and gives a
relatively planar structure between DHB group and CaO group. The spectral analysis together with the excitation energy calculations using
the ZINDO program showed that the absorption band at 309 nm in Riparin III, absence in Riparin I, is assigned to the p/p* transition
associated mainly from the DHB. A long range charge-transfer (CT) transition, as the low-lying excited electronic state, S1 has been
calculated for both relaxants involving the non-bonding electron on carbonyl and/or amine group and the antibonding orbitals of aromatic
ring. The planar structure of Riparin III and its extensive electron delocalization may have an important role on the pharmacological action
mode and on the potency this MR as compared to those of Riparin I.
q 2005 Elsevier B.V. All rights reserved
