Estael Ochoa | University of Havana (original) (raw)
Papers by Estael Ochoa
Revista Cubana de Química, 2005
Novel 4,7-dihydrothieno[2,3-b]pyridines 10a-d have been prepared in a one step procedure from the... more Novel 4,7-dihydrothieno[2,3-b]pyridines 10a-d have been prepared in a one step procedure from the readily available o-chloroformyl substituted 1,4-dihydropyridines 9a-d and ethyl mercaptoacetate in good yields. Semiempirical calculations reveal a favoured geometry with a boat conformation in the dihydropyridine system and a planar thieno ring. The calculated charge density values for the olefmic carbons (C5 and C6) are in agreement with the experimental push-pull effect observed in the 13C nmr.
![Research paper thumbnail of A straightforward synthesis and structure of unprecedented iminium salts of dihydropyrido[3,2-e][1,3]thiazines](https://attachments.academia-assets.com/83661307/thumbnails/1.jpg)
](Tetrahedron, 2006
Unprecedented 2-iminium chloride salts of 5,8-dihydro-2H-pyrido[3,2-e][1,3]thiazines derivatives ... more Unprecedented 2-iminium chloride salts of 5,8-dihydro-2H-pyrido[3,2-e][1,3]thiazines derivatives (8) were easily synthesized in one step from the corresponding o-chloroformyl-1,4-dihydropyridine (2) and thiourea. The structural study has been carried out by X-ray crystallography and theoretical calculations at the B3LYP/6-31G* levels and reveal that the new salts exhibit appropriate structural features to behave as calcium channel modulators.
Tetrahedron, 2000
A study of the behaviour towards alkylation of a series of benzoyl and furoylthioureas with 3,3-d... more A study of the behaviour towards alkylation of a series of benzoyl and furoylthioureas with 3,3-disubstitution has been carried out using NMR determinations. X-Ray data and semiempirical theoretical calculations demonstrated that the most stable conformation for these molecules is the so-called quasi-S. Also an explanation of the high selectivity towards the S-alkylation of these systems, based on the high contribution of the sulphur atom to the HOMO in acylthioureas is given for the title compounds. Steric factors are responsible for the difference between the percentages obtained for the S-alkylated product in 1-(4-methylbenzoyl)-3,3-diethylthiourea and 1-benzoyl-3,3dibenzylthiourea.
Tetrahedron, 2005
Thiocarbamates can react with weak bases, such as sodium or potassium carbonate, generating the c... more Thiocarbamates can react with weak bases, such as sodium or potassium carbonate, generating the corresponding anion, which can be represented through four plausible conformations as shown in Figure 1. 7 Molecular mechanics calculations onto N-acylthiocarbamate predict ...
Tetrahedron, 2000
Abstract—New substituted 4-aryl-2, 5-dioxo-8-phenylpyrido [2, 3-d] pyridazines 4a–f have been pre... more Abstract—New substituted 4-aryl-2, 5-dioxo-8-phenylpyrido [2, 3-d] pyridazines 4a–f have been prepared in one step from the corresponding arylidene substituted Meldrum's acid (1) and 5-amino-6-phenyl-3 (2H)-pyridazinone (2) in good yields. Semiempirical theoretical ...
Tetrahedron, 1999
A series of substituted 2,5-dioxo-l,2,3,4,5,5,7,8-octahydroquinolines have been synthesised from ... more A series of substituted 2,5-dioxo-l,2,3,4,5,5,7,8-octahydroquinolines have been synthesised from Meidrum's acid and dimedone in the presence of different aldehydes by following an approach similar to the one developed by Hantzch. The structure of these compounds has been thoroughly studied by X-ray crystallographic analysis and semiempirieal (AMI) and ab initio (HF/3-21G) methods, and two favoured conformations are possible. A good agreement is found between the theoretical and experimental values. The most stable conformation (A) in the solid state is also that favoured in solution, according to the proton coupling constant determined from Karplus' and Altona's equations and tH NMR spectroscopic experiments.
Tetrahedron, 1998
Pergamon Tetrahedron 54 (1998). 1240912420 TETRAHEDRON Structural Study of 3,4Dihydropyridones an... more Pergamon Tetrahedron 54 (1998). 1240912420 TETRAHEDRON Structural Study of 3,4Dihydropyridones and Furo[3,4b] 2(1H)pyridones as Potential Calcium Channel Modulators. Estael Ochoaa, Margarita Sue*, Yamila Verdeciaa, Beatriz Pita", b1B Nazario Martin , Margarita Quinteirob, Carlos ...
Polyhedron, 1997
The his(thiosemicarbazones) of glucose (GluTSCH,), galactose (GalTSCH,) and ribose (RibT-SCH,) we... more The his(thiosemicarbazones) of glucose (GluTSCH,), galactose (GalTSCH,) and ribose (RibT-SCH,) were prepared and characterized by spectroscopic ('H and "CNMR, UV. IR) methods. A complete assignment of the NMR signals was made using 'H-'H COSY ; "C'H COSY; "C COLOC and NOEDIF techniques, complemented with theoretical calculations. Metal complexes with the general formula [M(his TSC)], where M = Cu", Ni" and bisTSC = anion of the monosaccharide his(thiosemicarbazones). were prepared and characterized. The X-band ESR powder spectra of the copper(H) complexes show a rhombic distortion and the solution (DMF) ESR spectra indicate significant axial interaction with solvent molecules. The presence of the monosaccharide residue enhances the complexes' water solubility and increases their biological potential. J"l 1997 Elsevier Science Ltd &JWW&: bis(thiosemicarbazones) * Authors to whom correspondence should be addressed. All chemicals were of high purity and used as purt On leave from Universidade Federal de Minas Gerais.
QSAR & Combinatorial Science, 2006
Hortensia Rodrígueza, Osnieski Martína, Estael Ochoaa, Margarita Suáreza*, Osvaldo Reyesb, Hilda ... more Hortensia Rodrígueza, Osnieski Martína, Estael Ochoaa, Margarita Suáreza*, Osvaldo Reyesb, Hilda Garayb, Fernando Albericioc and Nazario Martínd* a Laboratorio de Síntesis Orgánica, Facultad de Química, Universidad de La Habana, 10400-Ciudad Habana, ...
Magnetic Resonance in Chemistry, 2002
The 1 H and 13 C NMR spectroscopic data for alkyl 4-aryl-6chloro-5-formyl-2-methyl-1,4-dihydopyri... more The 1 H and 13 C NMR spectroscopic data for alkyl 4-aryl-6chloro-5-formyl-2-methyl-1,4-dihydopyridine-3-carboxylates were fully assigned by combination of one-and two-dimensional experiments (DEPT, HMBC, HMQC, COSY, NOE).
Magnetic Resonance in Chemistry, 2004
Boletín de la Sociedad Chilena de Química, 2001
3-carboxymethyl-4-(4-chlorophenyl) -2, 7, 7-trimethyl-5-oxo -1,4,5,6,7,8-hexahydroquinoleine C 20... more 3-carboxymethyl-4-(4-chlorophenyl) -2, 7, 7-trimethyl-5-oxo -1,4,5,6,7,8-hexahydroquinoleine C 20 H 22 O 3 N Cl cristallyzed from ethanol solution as transparent white crystal, the crystal belong to an monoclinic system with space group P21/n, with a= 9.331(2), b= 18.340(4) ...
Boletín de la Sociedad Chilena de Química, 2000
The crystal and molecular structure of the Methyl-2,7,7-trimethyl-4-phenyl-5-oxo-1,4,5,6,7,8-hexa... more The crystal and molecular structure of the Methyl-2,7,7-trimethyl-4-phenyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline -3 carboxylate, C 20 H 23 NO 3 , has been determined by X-ray diffraction. Crystals are monoclinic, space group P2 1 /n; a = 9.646(2), b = 16.586(2), c = 11.111(1) Å, b = ...
![Research paper thumbnail of Theoretical Study of the Highly Diastereoselective 1,3-Dipolar Cycloaddition of 1,4-Dihydropyridine-Containing Azomethine Ylides to [60]Fullerene (Prato's Reaction)](https://attachments.academia-assets.com/83661277/thumbnails/1.jpg)
](The Journal of Organic Chemistry, 2005
The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropir... more The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropiridine ring to C 60 was investigated by means of quantum mechanical calculations at the semiempirical AM1 and DFT (B3LYP/6-31G*) methods. The presence of two chiral centers and one chiral axis in the resulting fulleropyrrolidines leads to four possible [6,6] cycloaddition products. Formation of atropoisomers has also been considered. The transition-state structures were computed for the four different cycloaddition pathways to find out the lowest activation energy stereoisomer. In all cases, a frequency analysis and an IRC calculation were carried out to fully characterize the located transition-state structures. AM1 results and single-point energy calculations at the B3LYP/6-31G*// AM1 level for the four transition-state structures yield activation energies values below 5 kcal/ mol.
![Research paper thumbnail of Novel hexahydrofuro[3,4- b ]-2(1 H )-pyridones from 4-aryl substituted 5-alkoxycarbonyl-6-methyl-3,4-dihydropyridones](https://attachments.academia-assets.com/83661283/thumbnails/1.jpg)
](Journal of Heterocyclic Chemistry, 1996
Revista Cubana de Química, 2005
Novel 4,7-dihydrothieno[2,3-b]pyridines 10a-d have been prepared in a one step procedure from the... more Novel 4,7-dihydrothieno[2,3-b]pyridines 10a-d have been prepared in a one step procedure from the readily available o-chloroformyl substituted 1,4-dihydropyridines 9a-d and ethyl mercaptoacetate in good yields. Semiempirical calculations reveal a favoured geometry with a boat conformation in the dihydropyridine system and a planar thieno ring. The calculated charge density values for the olefmic carbons (C5 and C6) are in agreement with the experimental push-pull effect observed in the 13C nmr.
Tetrahedron, 2006
Unprecedented 2-iminium chloride salts of 5,8-dihydro-2H-pyrido[3,2-e][1,3]thiazines derivatives ... more Unprecedented 2-iminium chloride salts of 5,8-dihydro-2H-pyrido[3,2-e][1,3]thiazines derivatives (8) were easily synthesized in one step from the corresponding o-chloroformyl-1,4-dihydropyridine (2) and thiourea. The structural study has been carried out by X-ray crystallography and theoretical calculations at the B3LYP/6-31G* levels and reveal that the new salts exhibit appropriate structural features to behave as calcium channel modulators.
Tetrahedron, 2000
A study of the behaviour towards alkylation of a series of benzoyl and furoylthioureas with 3,3-d... more A study of the behaviour towards alkylation of a series of benzoyl and furoylthioureas with 3,3-disubstitution has been carried out using NMR determinations. X-Ray data and semiempirical theoretical calculations demonstrated that the most stable conformation for these molecules is the so-called quasi-S. Also an explanation of the high selectivity towards the S-alkylation of these systems, based on the high contribution of the sulphur atom to the HOMO in acylthioureas is given for the title compounds. Steric factors are responsible for the difference between the percentages obtained for the S-alkylated product in 1-(4-methylbenzoyl)-3,3-diethylthiourea and 1-benzoyl-3,3dibenzylthiourea.
Tetrahedron, 2005
Thiocarbamates can react with weak bases, such as sodium or potassium carbonate, generating the c... more Thiocarbamates can react with weak bases, such as sodium or potassium carbonate, generating the corresponding anion, which can be represented through four plausible conformations as shown in Figure 1. 7 Molecular mechanics calculations onto N-acylthiocarbamate predict ...
Tetrahedron, 2000
Abstract—New substituted 4-aryl-2, 5-dioxo-8-phenylpyrido [2, 3-d] pyridazines 4a–f have been pre... more Abstract—New substituted 4-aryl-2, 5-dioxo-8-phenylpyrido [2, 3-d] pyridazines 4a–f have been prepared in one step from the corresponding arylidene substituted Meldrum's acid (1) and 5-amino-6-phenyl-3 (2H)-pyridazinone (2) in good yields. Semiempirical theoretical ...
Tetrahedron, 1999
A series of substituted 2,5-dioxo-l,2,3,4,5,5,7,8-octahydroquinolines have been synthesised from ... more A series of substituted 2,5-dioxo-l,2,3,4,5,5,7,8-octahydroquinolines have been synthesised from Meidrum's acid and dimedone in the presence of different aldehydes by following an approach similar to the one developed by Hantzch. The structure of these compounds has been thoroughly studied by X-ray crystallographic analysis and semiempirieal (AMI) and ab initio (HF/3-21G) methods, and two favoured conformations are possible. A good agreement is found between the theoretical and experimental values. The most stable conformation (A) in the solid state is also that favoured in solution, according to the proton coupling constant determined from Karplus' and Altona's equations and tH NMR spectroscopic experiments.
Tetrahedron, 1998
Pergamon Tetrahedron 54 (1998). 1240912420 TETRAHEDRON Structural Study of 3,4Dihydropyridones an... more Pergamon Tetrahedron 54 (1998). 1240912420 TETRAHEDRON Structural Study of 3,4Dihydropyridones and Furo[3,4b] 2(1H)pyridones as Potential Calcium Channel Modulators. Estael Ochoaa, Margarita Sue*, Yamila Verdeciaa, Beatriz Pita", b1B Nazario Martin , Margarita Quinteirob, Carlos ...
Polyhedron, 1997
The his(thiosemicarbazones) of glucose (GluTSCH,), galactose (GalTSCH,) and ribose (RibT-SCH,) we... more The his(thiosemicarbazones) of glucose (GluTSCH,), galactose (GalTSCH,) and ribose (RibT-SCH,) were prepared and characterized by spectroscopic ('H and "CNMR, UV. IR) methods. A complete assignment of the NMR signals was made using 'H-'H COSY ; "C'H COSY; "C COLOC and NOEDIF techniques, complemented with theoretical calculations. Metal complexes with the general formula [M(his TSC)], where M = Cu", Ni" and bisTSC = anion of the monosaccharide his(thiosemicarbazones). were prepared and characterized. The X-band ESR powder spectra of the copper(H) complexes show a rhombic distortion and the solution (DMF) ESR spectra indicate significant axial interaction with solvent molecules. The presence of the monosaccharide residue enhances the complexes' water solubility and increases their biological potential. J"l 1997 Elsevier Science Ltd &JWW&: bis(thiosemicarbazones) * Authors to whom correspondence should be addressed. All chemicals were of high purity and used as purt On leave from Universidade Federal de Minas Gerais.
QSAR & Combinatorial Science, 2006
Hortensia Rodrígueza, Osnieski Martína, Estael Ochoaa, Margarita Suáreza*, Osvaldo Reyesb, Hilda ... more Hortensia Rodrígueza, Osnieski Martína, Estael Ochoaa, Margarita Suáreza*, Osvaldo Reyesb, Hilda Garayb, Fernando Albericioc and Nazario Martínd* a Laboratorio de Síntesis Orgánica, Facultad de Química, Universidad de La Habana, 10400-Ciudad Habana, ...
Magnetic Resonance in Chemistry, 2002
The 1 H and 13 C NMR spectroscopic data for alkyl 4-aryl-6chloro-5-formyl-2-methyl-1,4-dihydopyri... more The 1 H and 13 C NMR spectroscopic data for alkyl 4-aryl-6chloro-5-formyl-2-methyl-1,4-dihydopyridine-3-carboxylates were fully assigned by combination of one-and two-dimensional experiments (DEPT, HMBC, HMQC, COSY, NOE).
Magnetic Resonance in Chemistry, 2004
Boletín de la Sociedad Chilena de Química, 2001
3-carboxymethyl-4-(4-chlorophenyl) -2, 7, 7-trimethyl-5-oxo -1,4,5,6,7,8-hexahydroquinoleine C 20... more 3-carboxymethyl-4-(4-chlorophenyl) -2, 7, 7-trimethyl-5-oxo -1,4,5,6,7,8-hexahydroquinoleine C 20 H 22 O 3 N Cl cristallyzed from ethanol solution as transparent white crystal, the crystal belong to an monoclinic system with space group P21/n, with a= 9.331(2), b= 18.340(4) ...
Boletín de la Sociedad Chilena de Química, 2000
The crystal and molecular structure of the Methyl-2,7,7-trimethyl-4-phenyl-5-oxo-1,4,5,6,7,8-hexa... more The crystal and molecular structure of the Methyl-2,7,7-trimethyl-4-phenyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline -3 carboxylate, C 20 H 23 NO 3 , has been determined by X-ray diffraction. Crystals are monoclinic, space group P2 1 /n; a = 9.646(2), b = 16.586(2), c = 11.111(1) Å, b = ...
The Journal of Organic Chemistry, 2005
The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropir... more The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropiridine ring to C 60 was investigated by means of quantum mechanical calculations at the semiempirical AM1 and DFT (B3LYP/6-31G*) methods. The presence of two chiral centers and one chiral axis in the resulting fulleropyrrolidines leads to four possible [6,6] cycloaddition products. Formation of atropoisomers has also been considered. The transition-state structures were computed for the four different cycloaddition pathways to find out the lowest activation energy stereoisomer. In all cases, a frequency analysis and an IRC calculation were carried out to fully characterize the located transition-state structures. AM1 results and single-point energy calculations at the B3LYP/6-31G*// AM1 level for the four transition-state structures yield activation energies values below 5 kcal/ mol.
Journal of Heterocyclic Chemistry, 1996