Análise estrutural de complexos de Zn com inibidores da enzima carboxipeptidase - ECA

Abstract

The mechanism of action of the angiotensin-converting enzyme (ACE) inhibitors antihypertensive drugs captopril, lisinopril and enalapril is related to the formation of a (in vivo) complex with the catalytic Zn2+ ion present at the active site of ACE. Thus, this work consisted in synthesis and structural characterization of three complexes of Zn2+ with the drugs captopril and lisinopril to observe whether in vitro the coordination sites of these drugs is similar to that suggested in vivo. Furthermore, it was synthesized the captopril disulfide dimer and evaluated the stability of drug captopril in relation the formation of its dimer. A salt formed by active principle enalaprilat ion and potassium ion and the form II of enalapril maleate were obtained. All compounds formed (with exception of MEFormaII) were characterized by vibrational spectroscopy techniques (IR and Raman) and elemental analyses for C, H and N, and the LISZn1 and LISZn2 complexes were also characterized by thermal analysis. Some compounds were analyzed by single crystal and powder X-ray diffraction. In the crystal structure of the CAPZn complex, the coordination sphere of Zn2+ ion showed a tetrahedral geometry. Each Zn2+ center is coordinated to four captopril ligands by two oxygen atoms of the carboxylate group and two sulfur atoms of the sulfhydryl group. Therefore, the interaction in vitro between the captopril drug and Zn2+ ion was similar to which is suggested in vivo, since the coordination of captopril drug occurred by the sulfur atom. CAPZn crystallized in a non-centrosymmetric space group, P41 and a three-dimensional coordination polymer was formed. The study of ACE enzyme interaction with the drug captopril was also mimicked by analyzing distribution of the electron density of CAPZn complex, which analyzed the character of the bond of metal ion and the occupation of d orbitals. Two new zinc complexes with the lisinopril drug were obtained from different synthesis. The synthetic differences led to the formation of compounds with significant structural differences since LISZn1 is amorphous while LISZn2 is crystalline. The crystal structure of LISZn2 complex was determined by X-ray diffraction technique. The complex exhibited the lisinopril drug coordinated to a Zn2+ ion by the oxygen atoms of the carboxylate and carbonyl groups as well as the primary and secondary amine nitrogen atoms. The interaction in vitro between the lisinopril drug and Zn2+ ion in LISZn2 was similar in some aspects to which is suggested in vivo, since the coordination of lisinopril drug occurred by the oxygen atom of central carboxylate group. This complex crystallized in a trigonal noncentrosymmetric space group (P32), and a one-dimensional coordination polymer was formed. This structure obtained is an example of twinning by inversion merohedry. It could not be solved by routine methods. DISCAP was obtained under hydrothermal conditions and crystallized in acentric space group P21. The crystal packing is stabilized by intramolecular and intermolecular hydrogen bonds. The study of the stability of the captopril compound was conducted by obtaining Raman spectra and diffractograms of drug over time with air exposure. The quantification of crystalline phases present in the sample captopril drug exposed for 52 weeks to the air through the Rietveld method demonstrated that the quantity captopril and captopril disulfide in the sample are 95 and 5%, respectively. DFT calculations in the solid state were performed for captopril and DISCAP. The results indicated that the DISCAP is approximately 30 kcal mol-1 more stable than captopril. The polymorphic form II of enalapril maleate (MEFormaII) was obtained and compared to the form I. The main difference between the polymorphic forms refers to the conformation of enalapril molecule, observed mainly in torsion angle C10-O1-C11-C12, relative to the ester group. The vibrational spectra of the salt formed by active principle enalaprilat ion and potassium ion (HIDROME) showed the absence of bands related to 𝜈(𝐶𝑂)𝑚𝑎𝑙𝑒𝑎𝑡𝑒, 𝜈(𝐶𝑂)𝑒𝑠𝑡𝑒𝑟, 𝜈(𝐶𝐶𝑂)𝑒𝑠𝑡𝑒𝑟 and 𝜈(𝐶𝐶𝑂)𝑎𝑐𝑒𝑡𝑎𝑡𝑒. This is an indication that the maleate ion is not present in compound formed and that the ester group may have been hydrolyzed. The investigation of the crystal structures obtained provided the coordination modes these ligands to the Zn2+ ion, in addition to the metal-ligand ratio in complexes formed and molecular interactions responsible for the stabilization of the crystalline solid. This investigation contributed to a better understanding of how occurs the interaction ACE-drug in human organism.