Angelina Flores-Parra

Boron coordination compounds derived from organic molecules of biological interest

Abstract Herein we describe our findings in the study of new boron coordination complexes derived from organic molecules of biological interest. The reported compounds have a coordinative bond between an acidic tricoordinated boron and a nitrogen, oxygen, sulfur or phosphorus atom. It is a summary of 17 years of investigation on this subject in our department. We are interested in the study of the boron coordination effects on organic molecules, in their stereochemistry, electronic density, atomic hybridization and spectroscopic behavior.

NMR study of the effect of nitrogen-borane coordination on the conformational equilibrium of six membered ring heterocycles.

Abstract The syntheses, conformational and spectroscopic studies of N-borane adducts of 14 nitrogen containing six-membered ring heterocycles are reported. It was found that borane can act as a conformational and configurational locking agent. In addition, it can be very helpful for the assignment of the chemical shifts of other atoms or groups in the molecule as well as to ascertain the configuration at substituted carbons.

Chlorination reactions of ephedrines revisited. Stereochemistry and functional groups effect on the reaction mechanisms

The stereochemistry of the chlorination reactions with SOCl2 of free ephedrine and pseudoephedrine and their hydrochlorides, oxamides and sulfonamides was analyzed. Chlorination of free and hydrochloride erythro isomers occurs with 100% inversion of configuration at C-1 (S N2 mechanism). Chlorination of oxamides and sulfonamides of erythro isomers occurs with retention of the configuration at C-1, (S Ni mechanism). Chlorination reactions in all threo isomers and derivatives hydrochlorides, oxamides or sulfonamides gave the same ratio of erythro (40%) and threo isomers (60%) (SN1 mechanism). Treatment of the isomeric mixture of the chlorodeoxyephedrine and chlorodeoxypseudoephedrine hydrochloride in DMSO with HCl changes the isomeric ratio, increasing the erythro isomer content (65%). Using the erythro ethanolamines it is possible to arrive stereoselectively at the erythro chloroamines if the compound is previously tosylated or converted to the amide, or to the threo chloroamines if the compound is directly chlorinated with SOCl2.

Antioxidant Activity of Butyl- and Phenylstannoxanes Derived from 2-, 3- and 4-Pyridinecarboxylic Acids

In vitro antioxidant activity for 12 stannoxanes derived from Ph3SnCl (compounds 1-3), Ph2SnCl2 (compounds 4-6), Bu3SnCl (compounds 7-9), and Bu2SnCl2 (compounds 10-12), was assayed qualitatively by the chromatographic profile with 1,1-diphenyl-2-picrylhydrazil (DPPH) method and by two quantitative methods: the DPPH radical scavenging activity and Ferric-Reducing Antioxidant Power (FRAP) assays. The results were compared with those obtained with the starting materials 2-pyridine- carboxylic acid (I), 3-pyridinecarboxylic acid (II) and 4-pyridinecarboxylic acid (III), as well as with standard compounds, such as vitamin C and vitamin E, respectively. The in vitro antiradical activity with DPPH of diphenyltin derivative 5 showed a very similar behavior to vitamin C at a 20 μg/mL concentration, whereas according to the FRAP method, compound 8 was better. This difference is due to the mechanism of the antioxidant process. The Structure-Activity Relationships (SAR) for both methods is also reported.

New chiral heterocycles: 5-[(r)-(+)-1′-methylbenzyyl-1,3,5-dithiazine and 3-7-di-[(R)-(+)-1′-methylbenzyu-3-7-diaza-1,5-dithiacyclooctane. Conformational studies and their reactions with borane.

Abstract We report herein the syntheses of a new 5-[(R)-(+)-1′-methylbenzyl]-1,3,5-di- thiazine 1 , the 5-isopropyl-1,3,5-dithiazine 2 and the 3,7-di-[(R)-(+)-1′-methylbenzyl]- 3,7-dlaza-1,5-dithiacyclooctane 3 , two of them ( 1 and 3 ) are new sulfur and nitrogen heterocycles bearing a chiral N-substituent. Compounds 1 and 2 were found in conformational equilibrium when observed at rt at 1 H-270 MHz or 13 C-67.8 MHz, when cooling a preferred chair conformation was observed with the N-substituent in the axial position. Heterocycle 3 was in an anchored crown conformation at rt. A conformational study of ring inversions for 1 and 3 was performed and their thermodynamic data were obtained, AG = 48.1 ± 0.8 for 1 and ΔG = 64.8± 1.2 kJ/mol for 3 . The reactivity of 1-3 with BH 1-3 THF was investigated, the N- or S-BH 3 adducts were not stable, the reactions afforded cleanly the N-borane-N-dimethyl-N-alkylamine adducts. The reaction of 3 with BD 3 gave the N-BD 3 adduct of [CH 2 D] 2 N-CH[CH 3 ]C 6 H 5 . An X-ray diffraction study of 3 confirmed its crown conformation with the N-substituents in pseudo-axial position.

Thiazaborolidines and BH3 adducts derived from thioephedrines

Abstract The synthesis of 1,3,2-thiazaborolidine and 2,3-dihydro-2,1,3-borathiazolidines from reaction of ephedrine disulfide and 3,4-dimethyl-5-phenyl-1,3-thiazolidine-2-thione with BH 3 -THF is reported. The two reactions afforded optically active borohydride heterocycles. The X-ray diffraction structure of (1 R ,2 R )-(−)-chlorodeoxy- pseudo -ephedrine hydrochloride, (1 R ,2 R )-(−)-thiosulfonic d deoxy- pseudo -ephedrine and (3 S ,4 R ,5 R )-(+)-dihydro-3,4-dimethyl-5-phenyl-2,1,3-borathiazolidine are reported.

NEW PERHYDRODITHIAZINES, NMR AND X-RAY DIFFRACTION STUDIES

Abstract A series of new perhydro-1,3,5-dithiazines have been prepared: 1,1′-bis-[5-(perhydro-1,3,5-dithiazinyl)]dimethylsulfide 2, bis-[5-(perhydro-1,3,5-dithiazinyl)]methane 3, 1,2-bis-[5-(perhydro-1,3,5-dithiazinyl)]ethane 4, 1,3-bis-[5-(perhydro-1,3,5-dithiazinyl)]propane 5, 1,4-bis-[5-(perhydro-1,3,5-dithiazinyl)]butane 6, 1-[5-perhydro-1,3,5-dithiazinyl)]-3-[4-morpholinyl]propane 7, and 1,1′-[5-(perhydro-1,3,5-dithiazinyl)]-3,3′-[1,4-piperazinyl]propane 8. The structure of all compounds was studied by 1H and 13C NMR and molecular mechanics calculations. An X-ray diffraction study was performed on compounds 5-methyl-perhydro-1,3,5-dithiazine 1a and 5-tert-butyl-perhydro-1,3,5-dithiazine 1b and 5–7. In the X-ray diffraction studies and in the molecular mechanics calculation it was found that all the six-membered rings were in a chair conformation and that in all the studied perhydro-1,3,5-dithiazines the substituent at the nitrogen atom was in the axial position, even in spite of a strong steric hindr...

BHδ––δ+HC Interactions inN-Borane andN-Chloroborane Adducts Derived from 1,3,5-Heterocyclohexanes

The molecular structures of 5-methyl-1,3-dithia-5-aziniumcyclohexane iodide, 5-chloroborane-5-methyl-1,3-dithia-5-azacyclohexane, 3,5-bis(borane)-3,5-dimethyl-1-thia-3,5-diazacyclohexane, and 1-borane-1,3,5-trimethyl-1,3,5-triazacyclohexane were determined by X-ray diffraction studies. Interactions between hydridic and protic hydrogen atoms are present when the distances between hydridic and protic hydrogen atoms are shorter than 265 pm and angles for B–N–C bonds are smaller than 107.6(3)°. These interactions explain the conformation of the borane adducts in the solid state.

N-BH3 adducts of trialkyl-1,3,5-triazacyclohexanes with stable stereogenic nitrogen atoms, stereochemical study

Abstract The syntheses and stereochemical studies of N-BH 3 adducts of trialkyl-1,3,5-triazacyclohexanes [ 1 , R= CH 3 ; 2 . R= iso -C 3 H 7 : 3 . R=CH(CH 3 )(C 6 H 5 ) (R); 4 , R= tert -C 4 H 9 ] are reported. Different reagent ratios were used in order to obtain mono- and di -N-borane adducts. Tri-N-borane adducts were never observed: di -N-borane adducts were formed with triazine 1 and 2 whereas 3 and 4 afforded only the mono -boranes. It appears that low steric strain is an important factor in the synthesis of these compounds. Borane addition produced in all cases ring and nitrogen conformationally stable compounds which were studied by NMR. All the reactions were 100% stereoselective affording one isomer in each reaction.

Preparation of new quinic acid boron esters in aprotic media

Abstract The syntheses, structure and reactivity of several boron derivatives of quinic acid, obtained in aprotic media, show that these boron heterocycles are useful intermediates, since they provide an alternative route to functionalize the quinic acid in a different way as when using dioxolane derivatives. Some new dioxolane derivatives of quinic acid and free quinide, as well as the lactone of quinic acid (6), were prepared in very high yields. The conformations of all new compounds were established from 1H NMR measurements.