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D Kocjan

Publications and source records attributed to D Kocjan.

10 recordsLinked to original sources
PubMed2001

Effect of column temperature on the behaviour of some angiotensin converting enzyme inhibitors during high-performance liquid chromatographic analysis.

The chromatographic behaviour of the ACE inhibitors lisinopril, enalapril and its two degradation products, enalaprilat (hydrolytic degradation product) and diketopiperazine (DKP) (cyclization degradation product) was studied as a function of column temperature and pH of the mobile phase. The rate of isomerization (which influences the peak shape or even peak splitting during chromatographic analysis) increases with temperature. The shape of the chromatographic peak for enalapril, enalaprilat and lisinopril is also pH dependent. At high temperature (80 degrees C) and low pH (pH=2) all studied compounds appear on the chromatogram as a narrow chromatographic peak. Chromatographic peaks become broader or they split by lowering the column temperature. Enalapril appears at 6 degrees C on the chromatogram in two peaks which belong to its cis- and trans-rotation isomers. Separation of the rotamers was confirmed by NMR spectroscopy.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Reactivity of anomeric 1alpha- and 1beta-pentofuranosyl azide derivatives in ammonia chemical ionization.

Electron impact (EI), fast atom bombardment (FAB) and ammonia chemical ionization [CI(NH3)] mass spectrometry were applied with the aim of differentiating between the anomeric 1alpha- and 1beta-azidopentofuranosyl derivatives. Calculated ammonium affinities [AA(M)] and proton affinities [PA(M)] show that beta-anomers have higher affinities for H+ and NH4+ ions than alpha-azides. Protonated molecules, obtained by CI(NH3) of azidofuranosyl derivatives, lose HN3 giving abundant furanosyl (S+) ions. Ammonia solvation of MH+ ions competes with the previous reaction producing the [SNHN2NH3]+ ion, a competitive product to the ammonium-attached [SN3NH4]+ ion. The fragmentation pathways of the stable and metastable [MNH4]+, MH+ ions, and several other important fragment ions, were determined using mass analyzed ion kinetic energy spectrometry (MIKES). The abundance of the [SN3NH4]+ and/or [SNHN2NH3]+ ions was found to correlate inversely with the exothermicity of ammonia solvation of the MH+ ion. The abundance of the fragment ions [SNHNH3]+, [SNH3]+ and SNH+ in some examples correlates with the exothermicity of the corresponding [MNH4]+ and MH+ parent ion formation. The fragment ions SNH3+ and SNHNH3+ can be formed, at least in part, in the ammonia solvation reaction of the S+ and SNH+ ions taking place within the high-pressure region of the CI ion source.

Journal Article↗
PubMed1994

On the interaction of the aromatic part of dopaminergic agonists with the receptor.

Structure-activity analysis of some selected, structurally diverse dopaminergic agonists that interact presumably with the D-2 receptor subtype was based on matching the minima of molecular electrostatic potential. Congruent superimpositions may indicate that the aromatic or heterocyclic portions of the structure interact with the receptor via pi- or lone pair electron density. The interaction of the aromatic or heterocyclic XH (X = O, N) group or substituent as a hydrogen bond proton donor seems not to be essential for binding and activating the dopamine receptor.

Dopamine Agents↗
PubMed1986

The biologically active conformation of ergot alkaloids.

Molecular mechanics and NMR studies of the D ring conformation of ergot alkaloids demonstrate that both D1 and D2 forms may exist in solution. The comparison of the geometric parameters defining the spatial relations between the aromatic moieties and the basic nitrogen of conformationally restricted dopamine analogs, and that of ergolene, shows the D1 conformation to be the bioactive one.

Dopamine↗
PubMed1986

Dopaminergic pharmacophore of ergoline and its analogues. A molecular electrostatic potential study.

Spatial correspondence between apomorphine, a prototype dopaminergic (DA) drug, and ergoline and some of its (partial) analogues were derived by matching their molecular electrostatic potential (MEP) patterns surrounding the aromatic moieties with respect to the coincident aliphatic N atoms. The MEP patterns were calculated from ab initio wave functions of model molecules. The congruent superimpositions of the molecular frameworks obtained between apomorphine and DA active ergoline analogues might corroborate the hypothesis that they bind with the same receptor sites when activating certain subtypes of the DA receptor.

Apomorphine↗
PubMed1983

Conformationally restricted dopamine congeners--a molecular mechanics-based study.

Potential energies of several systems containing the phenylethylamine fragment were computed by the QCFF/PI method and some of them also by the PCILO method. The systems considered are: octahydrobenzo [f]- and [g]-quinolines, aporphine, 1-phenylbenzazepine, 4-phenyltetrahydroisoquinoline, 3-phenylpiperidine and 9-aminodihydrophenanthrene. No common set of torsion angles defining the stereostructure around the amine head is apparent if only the lowest energy conformations are considered. Leaving out the orientation of the N-CH3 group, and considering also some higher energy conformations, two groups of systems may be formed, A and B, the members of which are congruent amongst themselves in parameters defining the spatial relations of the amine site and the catechol ring, and in the orientation of the N+-H bond. The stereostructure of the rigid representatives of group A is postulated to be the one required by the brain and cardioaccelerator nerve receptor. A corresponding postulate for the vascular bed DA receptors cannot be made since systems forming group B, the derivatives of which are active both on brain and vascular bed receptors, have more conformation space and, moreover, they carry additional potential anchoring groups.

Chemical Phenomena↗
PubMedDate not supplied

Conformational study of catecholamines in solution.

Conformations of noradrenaline, dopamine and ephedrine have been studied in aqueous solutions using high resolution PMR spectroscopy. We found that for dopamine the mole fraction of trans rotamer is increased if pH is changed from acidic to basic while for noradrenaline and ephedrine the opposite trend is observed: gauche rotamer forms of the side chain become more populated. These changes are discussed in relation to the role of the benzylic hydroxyl group for conformation and/or binding to a receptor site in the biophase.

Dopamine↗