Pyridine fragments

Further development in the chemistry of oxazolidinone antibacterials was based mainly on the assumption that the 4-pyridyl moiety of one of Dupont s lead compounds, E-3709, might be amenable to replacement by suitably saturated heterocyclic bioisosteres [48]. This assumption was based on an example in which successful replacement of the piperazine ring system in the quinolone antibacterials, such as ciprofloxacin, with a pyridine fragment, such as seen in Win-57273, results in improvement of both the antibacterial and the pharmacokinetic profiles of the compounds. Similarly, as in the case of ciprofloxacin and Win-57273, it was predicted that the presence of a small but highly electron-withdrawing fluorine atom would be tolerated at the meta position(s) of the central phenyl ring, and would confer enhanced antibacterial activity and/or other desirable properties to the targeted oxazolidinones, as shown in Fig. 3. 

Physicochemical properties rather than reactivities were also explored. Molecular electrostatic potential (MEP) was calculated for the [l,2,4]triazolo[4,3- ]pyridine fragment 23, according to the CHELPG algorithm. This afforded a prediction of its H-bond acceptor ability in view of the synthesis of p38 MAP kinase inhibitors <2005JME5728>. Tautomerism was also examined for compound 24, also postulated as two possible acyclic structures. The ab initio self-consistent field (SCF)-calculated energies support 24a as the most stable tautomer <1999MRC493>. 

Phenyldesylamine,21 when heated under reflux with phenylhydrazine in acetic acid, forms the 2,4,5-triphenyl-2,5-dihydro-lH-l,2,3-triazole 10 (Scheme 6).22 The 2-pyridyldesylamine21 leads to the same triazoline (10), with the pyridine fragment being lost during the cyclization in place of the benzene.22... 

Approach J is often used in organic synthesis and assumes the formation (sometimes, stepwise) of the N(l)-C(2) and C(4)-C(5) bonds of the pyridine fragment in reactions of 3-aminothiophenes with various 3C-components. In particular, this type... 

The construction of a thieno[3,2-Z>]pyridine by pathway M involves the successive formation of the N(l)-C(2) and C(3)-C(4) bonds of the pyridine fragment. Various 3-aminothiophene-2-carboxylic acid derivatives are most often used as the starting reagents with 2C-components, which introduce carbon atoms C(2) and C(3) into the pyridine ring. For example, the reaction of amino ester 155 with dimethyl acetylenedicarboxylate (156) involves intramolecular cyclocondensation followed by hydrazinolysis to give derivatives of the new heterocyclic system thieno[2, 3 5,6] pyrido[2,3-<7]pyridazine (157) (1991JHC205, 1990SPH203). 

Template effect of Cu(I) in synthesis of catenanes and molecular knots possessing pyridine fragments 92BSF113. 

Bridged bipyridines and terpyridines, fused systems with several pyridine rings or with indole and pyridine fragments simultaneously, rigid pyridino-phanes 91T6851. 

Synthesis of molecular cavities with fused pyridine fragments 92SL13. 

Proferrorosamine A.—Further information23 on the biosynthesis of the bacterial metabolite proferrorosamine A (14), which is known to derive from picolinic acid,24 is that [l-14C]glycerol is more extensively incorporated into the pyrrolidine than the pyridine fragment of (14). 

Acetylenes allenes. Nitrimines, prepared from ketoximes and nitrous acid, on acylation with acetic anhydride and pyridine with catalysis by 4-dimethylamino-pyridine fragment to alkynes and/or allenes. ... 

Total synthesis of streptonigrin and related antitumor antibiotics with quinoline and pyridine fragments 04T3539. 

AB 3413 cm characteristic for valence vibrations of NH pyridine group (Figs. 1, 2) and AB at 1591, 1567, 1475 and 1439 cm corresponding to valence vibrations of-C=C and -C=N- bonds of pyridine ring are presented in the spectra of chitosan modified with pyridine fragments. 

As shown in Table 2, catalyst N°1 exhibited a rather low selectivity. Introducing the second metal in chitosan (Pb or Zn) as well as pyridine fragments (catalysts N°5,6) improved the selectivity regarding cis-l,4-butenediol. However, the second stage rate remained almost the same. 

Pyridine reacts with phosgene to form a complex containing two pyridine fragments per carbonyl chloride. 

The preparation of 45 was used by Verducci as the benchmark reaction to check polymer 43 containing 4-piperidine pyridine fragments. The activity of this catalyst used in 20mol.% was lower than that of DMAP. Although the catalyst was recycled ten times a 30% decrease in its efficiency was observed. The use of different spacers did not modify significantly the results, but the catalytic activity was clearly decreased by raising the catalyst loading [185]. 

Dendrimers based on electroactive metal complexes with pyridine fragments 01CCC1. 

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