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Chemistry
Published in Stephen P. Coburn, The Chemistry and Metabolism of 4′-Deoxypyridoxine, 2018
While the Diels Alder condensation between oxazole derivatives and fumaric or mal-eic acid esters139 has received general acceptance as one of the best routes to the total synthesis of pyridoxine, there has been only one published attempt to use this procedure for the synthesis of deoxypyridoxine.564 Reacting 4-methyloxazole with ethyl crotonate in a sealed tube at 90°C for 20 hr produced 4′-deoxypyridoxine in only 10% yield. The possibility of obtaining 5′-deoxypyridoxine in addition to or instead of 4′-deoxypyridoxine may be one factor in the low yield. Ethyl crotonate is also a less active dienophile than ethyl fumarate. In our laboratory we have attempted an analogous synthesis by reacting 4-methyl-5-ethoxyoxazole with crotonyl chloride, crotonalde-hyde, or ethylcrotonate. While ultraviolet spectroscopy suggests that the oxazole reacts, we have been unable to isolate the desired product. Padyukova et al.380 have used the Diels Alder condensation to obtain a 24% yield of some B6 analogs after reacting for 10 days at room temperature. The details of the synthesis of a 5′-deoxy-pyridoxine derivative are presented later and may provide some ideas for improving the effectiveness of the Diels Alder condensation. In one case the yield was increased to 48% and the time reduced to 5 hr at room temperature when the pressure was increased to 10,000 atm.
Drug Discovery: From Hits to Clinical Candidates
Published in Divya Vohora, The Third Histamine Receptor, 2008
Sylvain Celanire, Florence Lebon, Holger Stark
In 2006, Neurogen entered the H3 arena with newly claimed chemical entities such as compounds 175 and 176 as representatives (no specific data) [207, 208]. Since their long-term involvement in the histamine H1/H3 field, scientists at Schering Corp. have identified novel nonimidazole H3 antagonists that do not belong to the classical aminopropoxyphenyl framework. Indeed, piperidinomethyl-aminopyridines (177a,b), and more recently amino-alkoxyphenyl-benzimidazole-based compounds (e.g., 178a hH3 pKi 9.0; 178b), have been claimed in a number of patent applications by this group (Figure 5.24) [209–212]. Involved in the histamine H1R field earlier, with the antihistaminic blockbuster drug Zyrtec® (cetirizine) for the treatment of allergic rhinitis, scientists at biopharmaceutical company UCB Pharma pursued their efforts toward the discovery of novel histamine H3 ligands. In two patent applications, novel oxazoline and oxazole-based structures have been reported, with compounds 179 and 180 as selected examples (no specific data described) [213, 214].
Chemical Methods of Amino Acid Sequence Analysis from Carboxy Terminal End
Published in Ajit S. Bhown, Protein/Peptide Sequence Analysis: Current Methodologies, 1988
At the Second International Conference on Solid Phase Methods in Protein Sequence Analysis in 1978, another approach to C-terminal sequencing was described by Previero and Coletti-Previero.30 This involved alcoholysis of an oxazole formed at the C terminus of a peptide. Dipeptides or tripeptides were immobilised by N-acylation with polyacrylyl chloride and esterified with methanol in the presence of a carbodi-imide. Cyclization to the oxazole was achieved by treating the ester with phosphorous pentachloride. The oxazole was then subjected to acid-catalyzed methanolysis, as shown in Figure 6, which released the C-terminal amino acid as its methyl ester, leaving behind the immobilized shortened peptide. The cleavage of the C-terminal amino acid was incomplete after one cycle, and the cumulative yield of four consecutive cycles was between 80 and 90%. Repetitive degradations were not performed. This procedure does not look very encouraging, judging by results obtained so far.
Review on Chemistry of Oxazole derivatives: Current to Future Therapeutic Prospective
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Sweta Joshi, Meenakshi Mehra, Ramandeep Singh, Satinder Kakar
The oxazoles structure other nitrogen and oxygen containing heterocycles resembles each other. The oxazole heteroatoms are structurally identical to the oxygen present in furan and the nitrogen in pyridine. The studies show that the nature of oxazole also intervenes as furan and pyridine. Oxazole is basic in nature and shows similarity to those of pyridine in some aspects [7]. Concurrently they show minimum resistance against oxidation and more resistance to acids as compared to pyridine, but they show some of the instability identical to furans. The oxazoles are thermally stable entity which differ from intensely volatile liquids and do not undergo decomposition at high boiling temperature. Presence of exocyclic double bond forms dienophile and N-substituted oxazole shows Diels alder reaction. These oxazolone rings show high electrophilic reaction centers for the attack of nucleophile. Oxazole hydrogen atoms become less acidic in the order C2> C5> C4. At C2, it was discovered that hydrogen has pka 20 acidity and a pkb 1.17 acidity [8].
Therapeutic potential of oxazole scaffold: a patent review (2006–2017)
Published in Expert Opinion on Therapeutic Patents, 2018
Ramandeep Kaur, Kezia Palta, Manoj Kumar, Meha Bhargava, Lalita Dahiya
Oxazole (1) is a well-known important heterocyclic motif characterized as 1,3-azole possessing oxygen and nitrogen atoms in 1,3 relationship of five membered ring. This was first reported by Hantzsch in 1887 and synthesized in 1947. Annuloline was the first demonstration of oxazole ring in nature. Benzo derivatives of oxazole are called as benzoxazole (2). Partially reduced oxazoles are called oxazolines and depending upon the position of the double bond are named as 2-oxazoline (3), 3-oxazoline (4), and 4-oxazoline (5), whereas, the fully saturated analog is called as oxazolidine (6). Oxazole is weakly basic liquid, miscible with water and organic solvents and has dipole moment of 1.5 D. Although the sextet of π-electrons is present in oxazole ring, its properties have demonstrated incomplete delocalization of π-electrons that attributes to its little aromaticity and greater dienic character. This lower aromaticity is not to be equated with instability [5–8].