Analyse conformationnelle de pyrazolines-1 substituées

Conformational analysis of 1-pyrazolines bearing different substituents on carbons 3 and 4 has been achieved by NMR. The use of the Karplus equation to explain the values of the coupling constants ³J(H₄? H₅) allows us to ‘check’ the existence of an equilibrium between two envelope conformations. The folding angle of the envelope, calculated on a model compound which is held in only one conformation, wad found to be near 36°. The ratio of the two conformers at room temperature is calculated for the various pyrazolines studied.     

Etude des formes fermées et ouvertes de spiropyrannes benzothiazoliniques en RMN 13C et 1H par transformée de Fourier

Benzothiazolinic spiropyrans, merocyanines and photomerocyanines, thermally stabilised to a high degree, have been studied by means of Fourier transform ¹H and ¹³C NMR. The results show the polarity of open forms such as merocyanines and photomerocyanines, their trans configuration, the alternation of the electronic density on the dimethine bridge between the ‘benzothiazolinic’ and ‘phenolate’ part of these molecules, and also a favoured configuration when photomerocyanines have an alkoxy or aryloxy group on the 3 position.     

Déconjugaison d'énones dérivées de sucres Communication préliminaire

Deconjugation of sugars enones. Preliminary Communication Branched-chain sugar enones 1 and 2 ( R = Ac) deconjugated toposelectively (only the E isomers reacting) to 3 . The same phenomenon was noted in the case of Z- 4 which gave E- 5 . The kinetic parameters of these reactions favored a concerted mechanism, i.e. a [1, 5]-sigmatropic shift.     

Utilisation d'ylides du phosphore en chimie des sucres. XII Dérivés du D-arabino-hexène-1-tétrol-3,4,5,6

The preparation of several kinds of derivatives of 1-substituted D -arabinc-hex-1-ene-3,4,5,6-tetrols is described. Some of these compounds, having a ‘pseudo-formyl’ group (? CH?CHCN, ? CH?CHSO₂CH₃) are ‘pseudo-aldehydo-sugars’. Their ability to react as aldehydo-sugars was examined in light of their ¹³C-NMR. spectra which provide information on their electron density at C(1) and C(2).     

Un nouvel exemple de transposition: l'épimérisation en C(3) d'hydroxy-3-δ1-pyrazolines dérivées de sucres

A Novel Example of Reversible Ring Opening: The Epimerization at C(3) of Sugar 3-Hydroxy-Δ¹-pyrazolines Reaction of 1 (either geometrical isomer) with hydrazine followed by in situ Ag₂O oxidation led to two pairs of interconverting isomers 4 ? 5 and 6 ? 7 . By the same treatment, (Z)- 10 and (or) (E)- 10 gave the pair 11 ? 12 . Acetylation of 4 ? 5 led to a non interconverting mixture of 8 and 9 . This fact, and the lack of incorporation of ¹⁸O when the epimerization took place in the presence of H₂¹⁸O indicated that the most probable mechanism consisted in a reversible ring opening ( D ? E ? F ). The kinetic parameters of these reactions are given and structural assignments proposed for the new compounds.     

A 1H NMR study of tautomerism in some 1-arylamino-3-aryliminopropenes

¹H n.m.r. spectra at ambient temperatures reveal that an equilibrium exists between the ‘all-trans’ and ‘all-cis’ isomers of some of the 1-arylamino-3-aryliminopropenes. The ‘all-cis’ isomer predominates in nonpolar solvents, whereas the ‘all-trans’ isomer is favoured in hydrogen bonding solvents. From a consideration of the magnitudes of the ³J coupling constants, it is reported that the ‘cis-trans’ isomer is the most stable form of the 4-nitrophenyl derivative in dimethyl sulphoxide.     

Equilibres conformationnels de glucides au niveau de liaisons s̀ sp2-sp3 C?C. II Dérivés d'hydrozones d'aldéhydo-sucres

A series of alkyl-and aryl-hydrazones of different types of aldehydo-sugars with blocked hydroxy groups have been studied, mainly by PMR. spectroscopy. No traces of the azoalkane or ene-hydrazine forms were detected; the hydrazones were found to exist only in the syn form, except for the cases where an intramolecular hydrogen bond between the ‘amino’ hydrogen of the hydazono group and an oxygen o the glycosyl group provides an extra-stabilization to the anti isomer. Most of these syn hydrazones seem to exist as an equilibrium of the ‘classical’ eclipsed rotamers. The influence of solvent polarity both on configurational and conformational equilibria has been examined. The factors which determine the relative stability of the conformers about a sp²-sp³ s? bond, particularly some kind of non-bonded attraction, are discussed.     

Structure moléculaire et propriétés moléculaires de quatre isomères de formule C8H10N4

The molecular structures of the three Meyer isomers [3-methyl-3-(5′-amino-3′-methyl-l-pyrazolyl)acrylonitrile; acetylacetonitrile azine; 2,5-dimethyl-7-aminopyrazolo[1,5-a]pyrimidine] have been compared with that of the fourth isomer, 2,7-dimethyl-5-amino-pyrazolo[1,5-a]pyrimidine. The CNDO/2 and CNDO/S calculations utilizing these geometries have been accomplished. These include electronic transitions, dipole moments, ionisation potentials, charge densities, bond ordres and total energies. The calculated values have been compared to some experimental data. Uv spectra, ¹³C chemical shifts, ¹H-¹H coupling constants and relative stability of the four isomers are included.     

Interactions intramoléculaires: XXIII—Constantes de couplage et interactions gauches avec un groupement t-butyle (cyclohexanones disubstituées 3, 4)

The ¹H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d₄) are analysed. By comparison of their ³J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH₃, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH₃)₃C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ₃₄ of about ?6°.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Conformation et spectrométrie de R.M.N.: II

The four isomeric 3-dimethylamino-trans-2-decalols-1,1,4,4-d₄ have been synthesised. Examination of PMR spectra of these compounds allows us to confirm the ‘flattened-chair’ conformation for the cis N(CH₃)₂^a OH^e isomer, whereas the remaining three conserve the double chair conformation. The same type of flattening is also observed in the case of the diaxial quaternary ammonium salt and is even more marked in the cis N(CH₃)₃^a OH^e isomer resulting in a ‘twist-chair’ conformation.     

Synthese von Glycerylätherphosphatiden 2. Mitteilung Herstellung von 2-O-Acetyl-1-O-[(Z)-9-octadecenyl] -sn-glyceryl-3-phosphorylcholin («Oleyl-PAF»), des Enantiomeren sowie einiger analoger,ungesättigter Verbindungen

Synthesis of Glyceryletherphosphatides, 2nd Communication. Preparation of 2-O-Acetyl-1-O-[(Z)-9-octadecenyl]-sn -glyceryl-3-phosphorylcholin (‘Oleyl-PAF’), of its Enantiomer and Some Analogous, Unsaturated Compounds Syntheses of the unsaturated glyceroletherphospholipid 1a as an olefin-analog of ‘Platelet Activating Factor’ (PAF) are described together with the methods for the preparation of the enantiomer 1′a , the corresponding ‘lyso compounds’ 1b and 1′b and their positional isomers 21a, 21′a, 26, 26′, 25, 25′ obtained on formally exchanging the attachment site of the functional groups at the glycerol moiety. Structural assignments and optical purity of the compounds are confirmed.     

Synthèse de nouveaux types de dérivés C-glycosyliques à partir de sucres acétyléniques ou de leurs équivalents synthétiques partiels

Synthesis of Novel Types of C-Glycosyl-derivatives from Acetylenic Sugars or Partial Synthetic Equivalents thereof The concept of synthetic equivalent is not unequivocal and, for example, α-fluoroenamines may behave in some cases as synthetic equivalents of ynamines and, in other situations, quite differently. Some uses of these α-fluoroenamines, ‘partial synthetic equivalents’ of ynamines, for the synthesis of C-glycosyl derivatives of coumarins, chromones, quinolines, quinolones, thietenes and isoxazoles are described. We also report the preparation of a series of mono- and diglycosylthiophenes by reacting HS^? with mono- and diglycosylbutadiynes. Acetylenic sugar derivatives have also been used for the synthesis of a diglycosylazaphosphorine and a spirooxolenone.     

Etude Stéréochimique par RMN 1H de Tetrahydropyrannes β-Chlorés α-Substitués

The ¹H NMR study of 2-alkyl-3-chlorotetrahydropyrans, obtained by reaction of Grignard reagents with a mixture of cis/trans-2,3-dichlorotetrahydropyrans, shows cis/trans configuration of two isomers in which the alkyl substituents are exclusively in the equatorial position. 3-Chloro-2-phenyltetrahydropyran exists in trans (eq-eq) configuration only. The ¹H NMR study of cis/trans 2-alkoxy (or aryloxy)-3-chlorotetrahydropyrans, obtained by reaction of alcohols or phenol with 2,3-dichlorotetrahydropyrans, shows the axial position of the alkoxy (or aryloxy) substituent.     

Untersuchungen zur Carotinoidzusammensetzung in Blüten der Gartenhybride Narcissus cvv ‘Golden Harvest’

Investigation of the Carotenoid Composition in the Petals of a Garden Hybrid Narcissus cvv ‘Golden Harvest’ The carotenoid composition of the petals of a yellow garden hybrid Daffodil is reported. As major compound (all-E)-lutein was isolated. As minor compounds phytoene, phytofluene, (all-E)-β-carotene, (9Z)-lutein, (9′Z)-lutein, (13Z)-lutein, violaxanthin, and luteoxanthin were identified. The position of the (Z)-double bond of the different isomers of lutein could be proved by ¹H-NMR spectroscopy.     

Studies in the Helicene Series NMR. Evidence of ‘Helicene-like’ Conformations in the cis 1,2-Diarylethylenes. Part XVII

The cis and trans isomers of eight 1,2-diarylethylenes, precursors of helicenes, have been studied by NMR. spectroscopy. The observed differences in chemical shifts, specific solvent effects and steric effects (bromo derivatives) can be explained by the contribution of ‘helicenelike’ conformers in the cis isomers.     

Diastéréotopies dans la série du benchrotrène

¹H and ¹³C spectra of mono-and disubstituted (benzene)-tricarbonylchromium complexes have been analysed. The influence of the substituents is discussed and special attention is paid to the diastereotopy resulting from different types of chirality. The racemic pseudosymmetric isomer and the two meso pseudoasymmetric isomers of the glycols (OC)₃CrC₆H₄(CHOHCH₃)₂ are compared. The stereochemical requirements are also examined.     

Differentiation of Boc‐protected α,δ‐/δ,α‐ and β,δ‐/δ,β‐hybrid peptide positional isomers by electrospray ionization tandem mass spectrometry

Two new series of Boc‐N‐α,δ‐/δ,α‐ and β,δ‐/δ,β‐hybrid peptides containing repeats of L ‐Ala‐δ⁵‐Caa/δ⁵‐Caa‐L ‐Ala and β³‐Caa‐δ⁵‐Caa/δ⁵‐Caa‐β³‐Caa (L ‐Ala = L ‐alanine, Caa = C‐linked carbo amino acid derived from D ‐xylose) have been differentiated by both positive and negative ion electrospray ionization (ESI) ion trap tandem mass spectrometry (MS/MS). MSⁿ spectra of protonated isomeric peptides produce characteristic fragmentation involving the peptide backbone, the Boc‐group, and the side chain. The dipeptide positional isomers are differentiated by the collision‐induced dissociation (CID) of the protonated peptides. The loss of 2‐methylprop‐1‐ene is more pronounced for Boc‐NH‐L ‐Ala‐δ‐Caa‐OCH₃ (1), whereas it is totally absent for its positional isomer Boc‐NH‐δ‐Caa‐L ‐Ala‐OCH₃ (7), instead it shows significant loss of t‐butanol. On the other hand, second isomeric pair shows significant loss of t‐butanol and loss of acetone for Boc‐NH‐δ‐Caa‐β‐Caa‐OCH₃ (18), whereas these are insignificant for its positional isomer Boc‐NH‐β‐Caa‐δ‐Caa‐OCH₃ (13). The tetra‐ and hexapeptide positional isomers also show significant differences in MS² and MS³ CID spectra. It is observed that ‘b’ ions are abundant when oxazolone structures are formed through five‐membered cyclic transition state and cyclization process for larger ‘b’ ions led to its insignificant abundance. However, b₁⁺ ion is formed in case of δ,α‐dipeptide that may have a six‐membered substituted piperidone ion structure. Furthermore, ESI negative ion MS/MS has also been found to be useful for differentiating these isomeric peptide acids. Thus, the results of MS/MS of pairs of di‐, tetra‐, and hexapeptide positional isomers provide peptide sequencing information and distinguish the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Réactions d'élimination présentées par des acides polyhydroxyadipiques

The tetrahydroxyadipic acids and one trihydroxyadipic acid have been methylated, using methyl iodide and silver oxide in the presence of dimethylformamide. In addition to Δ²-di- or tri-methoxyadipic esters and the products expected for a double E2 elimination, cis-trans α, α'-dimethoxymuconic ester was frequently the principal product. The proposed theoretical interpretations involve as intermediates either a silver complex or a lactonic compound. A few preferential conformations, based on NMR. data, are proposed.     

Der ‘Push-Pull’-Effekt von ‘Push-Pull’-Oligoacetylenen. Eine 13C-NMR-Untersuchung

The ‘Push-Poll’ Effect of ‘Push-Pull’ Oligoacetylenes. A ¹³C-NMR Investigation According to ¹³C-chemicaI shifts of ‘push-pull’ oligoacetylenes 1 – 4 , the ‘push-pull’ effect (i.e. π delocalization induced by ‘push-pull’ substituents) rapidly decays in this series. To correct for other than π -charge-density effects, Δδ values of symmetrically placed C-atoms of the oligoacetylene chain are discussed. Stereoelectronic resteffects (SER) of the substituents on terminal C-atoms of PP-ketones 1a – 3a and PP -esters 1b – 4b are estimated from the residual Δδ of the asymptotes of Fig. 3. Fig. 4 convincingly shows that Δδ values are dramatically decreasing with increasing number n of acetylene units between the push and pull substituents. Assignment problems of ‘push-pull’ triacetylenes 3 have been solved by ¹³C labelling of the CO group of 3a .