Search results for "BOX"

Asymmetric hydrogenation of an α-unsaturated carboxylic acid catalyzed by intact chiral transition metal carbonyl clusters – diastereomeric control o…

2020

Twenty clusters of the general formula [(μ-H)2Ru3(μ3-S)(CO)7(μ-P–P*)] (P–P* = chiral diphosphine of the ferrocene-based Walphos or Josiphos families) have been synthesised and characterised. The clusters have been tested as catalysts for asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid]. The observed enantioselectivities and conversion rates strongly support catalysis by intact Ru3 clusters. A catalytic mechanism involving an active Ru3 catalyst generated by CO loss from [(μ-H)2Ru3(μ3-S)(CO)7(μ-P–P*)] has been investigated by DFT calculations. peerReviewed

Muskelrelaxantien, 4. Mitt. Monoacylbutyroguanamine

1986

Die Umsetzung von Butyroguanamin (1) mit den Carbonsaureanhydriden 2a−f bei 80–120° fuhrt zu den Monoacylbutyroguanaminen 3a−f, deren Struktur durch IR-, 1H-NMR- und MS-Spektren untermauert wird. Unter den hier beschriebenen Verbindungen weisen insbesondere 3e muskelrelaxierende und antidiabetische und 3a trichomonazide und antivirale Wirksamkeit auf, wahrend mit 3b−d herbizide Wirkungen beobachtet werden. Muscle Relaxants, IV: Monoacylbutyroguanamines Reaction of butyroguanamine (1) with the carboxylic acid anhydrides 2a−f at 80–120°C leads to the monoacylbutyroguanamines 3a−f, the structure of which is supported by IR, 1H-NMR, and mass spectra. Among the compounds described here, particul…

Iron deficiency testing and treatment in heart failure: the eyes are useless when the mind is blind

2021

Definition, clinical implications, and rate of iron deficiency assessment and treatment in the Swedish Heart Failure Registry. FCM, ferric carboxymaltose; HF, heart failue; ID, iron deficiency; TSAT, transferrin sauration.

Susceptibility of Methyl 3-Amino-1H-pyrazole-5-carboxylate to Acylation

2009

Abstract In the search for a new method of synthesis of hybrid peptides with aminopyrazole carboxylic acid, we tried to force selective acylation at the aromatic amino group instead of at the ring nitrogen atom with fairly gentle acylating agents. The acylating agents used were acid anhydrides: acetic anhydride, tert-butyl pyrocarbonate, and 2-(2-methoxyethoxy)ethoxyacetic acid/dicyclohexylcarbodiimide. We succceded in acylation at this amino group with almost none at the ring nitrogen atom. Sometimes, however, acylation in small quantities at the ring nitrogen atom was observed as a by-product. To remove this by-product, imidazole was used. Thus, we were able to obtain the hybrid peptides …

A DFT Characterization of the Mechanism for the Cycloaddition Reaction between 2-Methylfuran and Acetylenedicarboxylic Acid

1999

The molecular mechanism for the cycloaddition reaction between 2-methylfuran and acetylenedicarboxylic acid (ADA) has been characterized using density functional theory methods at the B3LYP/6-31+G* theory level. An analysis of the results on the reaction pathway shows that the reaction takes place along a stepwise mechanism. The initial step corresponds to the nucleophilic attack of the C5 position of the furan ring to one carbon atom of the conjugated acetylenic system of ADA to give a zwitterionic intermediate. Closure of this intermediate along the nucleophilic attack of the other acetylenic carbon to the substituted C2 position of the furan ring affords the Diels−Alder cycloadduct. Alth…

Competition between decarboxylation and isomerization in the C3H5O 2+ energy surface. Justification of the experimental results by molecular orbital …

1994

In constrast with recent molecular orbital calculations on the decarboxylation of O-protonated 2-oxetanone, this experimental work indicates that no decarboxylation of this cation occurs in sulphuric acid solution up to 150°C, but instead a clean isomerization to protonated acrylic acid takes place. Parallel theoretical work shows that the gas-phase model is too crude to account successfully for the experimental facts obtained in acidic media. However, the latter are well reproduced when the effect of the solvent is taken into account. The present findings do not necessarily invalidate the reaction mechanism currently accepted to explain the rate enhancement and change of stereochemistry ac…

ARGININE, HISTIDINE AND TRYPTOPHAN IN PEPTIDE SYNTHESIS. THE IMIDAZOLE FUNCTION OF HISTIDINE

1989

Toward an understanding of the selectivity in domino reactions. A DFT study of the reaction between acetylenedicarboxylic acid and 1, 3-Bis(2-furyl)p…

2000

The mechanism of the domino reaction between acetylenedicarboxylic acid and 1,3-bis(2-furyl)propane has been theoretically studied in the framework of density functional theory. This domino process comprises two consecutive cycloaddition reactions: the first one is initialized by the nucleophilic attack of the C5 position of the furan ring to a conjugate position of acetylenedicarboxylic acid to give a zwitterionic intermediate, which by a subsequent ring-closure process affords an oxanorbornadiene intermediate. The second reaction is an intramolecular concerted cycloaddition of this intermediate to give the final dioxapentacyclic adduct. For the second cycloaddition, which corresponds to t…

A Simple Organocatalytic Enantioselective Synthesis of Pregabalin

2009

This paper describes a new procedure for the enantioselective synthesis of the important anticonvulsant drug Pregabalin, which shows biological properties as the (S) enantiomer only. The key step of the synthetic sequence is the Michael addition reaction of Meldrum's acid to a nitroalkene mediated by a quinidine derived thiourea. A variety of novel catalysts bearing different groups at the thiourea moiety were synthesized and tested. The most successful catalyst that incorporates a trityl substituent provided up to 75 % ee of (S)-4. The conjugate addition reaction was carried out on a multigram scale with low loadings of catalyst (10 mol-%). Moreover, the catalyst can be recycled showing th…

Synthesis of azamacrocycles via a Mitsunobu reaction

2005

Reaction of pernosylated diethylenetriamine and 2-substituted propane-1,3-diols in dry THF in the presence of triphenylphosphine and diisopropyl azodicarboxylate gives the corresponding protected 9-substituted 1,4,7-triazacyclodecanes. The Mitsunobu reaction was also used in the preparation of 3-substituted 1,5,9-triazacyclododecanes and macrocyclic pyridine derivatives.