Introduction Of Protecting Groups Research Articles

Synthetic Approaches to Unsymmetrically Substituted 5,7-Dihydroxycoumarins

The chemical equivalence of the hydroxy groups in the 5,7-dihydroxycoumarin core has challenged synthetic chemists to develop short and efficient strategies for the selective modification of one of the hydroxy groups leaving the second intact. Over the past 100 years, chemists have proposed various approaches to distinguishing between these two groups according to their reactivity. While the early syntheses included simple nonselective reactions of both hydroxy groups and the subsequent separation of mixtures of the 5-O- and 7-O-isomers formed, recent sophisticated approaches often include the introduction of protective groups for selective directing reactions or the completely controlled construction of the 5,7-dihydroxycoumarin framework by Horner–Wadsworth–Emmons reaction. This review discusses in detail approaches towards unsymmetrically substituted 5,7-dihydroxycoumarins as well as factors influencing 5-O vs. 7-O regioselectivity of reactions of 5,7-dihydroxycoumarins. This review covers all the literature since 1921 with an emphasis on recent works. This critical review may facilitate the synthesis of new drug candidates as well as the total synthesis of natural products.1 Introduction2 O-Modification of 5,7-Dihydroxycoumarins2.1 Alkylation/Alkenylation2.2 Acylation2.3 Sulfonylation2.4 Silylation2.5 Acylation Followed by Alkylation3 Other Approaches3.1 Synthesis from Substituted Phloroglucinol3.2 Synthesis from Derivatives of 2-Acylphloroglucinol4 Conclusion

Precise Synthesis of Functional Block Copolymers by Living Anionic Polymerization of Vinyl Monomers Bearing Nitrogen Atoms in the Side Chain

Precise synthetic methods to prepare functional block copolymers with heteroatoms (nitrogen, oxygen, sulfur, phosphorous, halogen, etc.) have received much attention for the fabrication of practical nanomaterials. Specifically, well‐defined materials containing nitrogen‐based functional groups show unique electrical, optical, and amphiphilic properties. To synthesize these products, living anionic polymerization is the most powerful method. However, the disruption of undesirable reactions is considered to be a great challenge in the anionic polymerization of functional monomers with heteroatoms. To overcome these problems, facile methods such as polymerization at low temperature, careful choice of additives and initiators, and the introduction of protective groups can be used. In this review, recent advances in the anionic polymerization of vinyl monomers with triphenylamine, carbazole, and pyridine moieties in the side chains will be discussed. Also covered is the morphological control of these polymers to obtain well‐defined block copolymers for practical applications such as organic memory devices and light emitting diodes. image

保護基導入によるPLA加水分解加速機構の発現可能性に関する分子シミュレーションを用いた検討

保護基導入によるPLA加水分解加速機構の発現可能性に関する分子シミュレーションを用いた検討

Metal Complexes of Biologically Important Ligands, CLXXII [1]. Metal Ions and Metal Complexes as Protective Groups of Amino Acids and Peptides – Reactions at Coordinated Amino Acids

The introduction of protective groups into multifunctional molecules, e. g. into amino acids for peptide synthesis, and their removal are one of the most important techniques and strategies in Organic Chemistry [2]. Amino acids, their anions and derivatives are versatile ligands, and the leading idea to protect the N- or C-terminus of amino acids by metal ions or by metal complexes has opened interesting chapters which reach from classical coordination and bioinorganic chemistry to modern organometallic and bioorganometallic chemistry [3]

9] Simple methods for preparing nicotinamide mononucleotide and related analogs

Publisher Summary This chapter describes the methods for preparing nicotinamide mononucleotide and related analogs. Nicotinamide mononucleotide (NMN) is a prerequisite in the preparation of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) analogs, of which the nonfunctional nucleotide moiety is to be modified; correspondingly, NMN analogs are necessary for preparing coenzyme models that have a modified functional moiety. There are two ways to prepare NMN: (1) cleavage of the dinucleotide NAD(P), by acid hydrolysis or by dinucleotide-nucleotidohydrolases (NAD-pyrophosphatases) and (2) total synthesis, starting with the nucleotide components nicotinamide, ribose, and phosphate. Nicotinamide nucleosides can be prepared from l-halogeno sugars and nicotinamide, or by the reaction of N1-(2,4-dinitrophenyl)-3-carba-moylpyridinium chloride with 1-amino sugars. In both cases, a mixture of anomeric nucleosides is obtained; the ratio of its constituents depends on the sugar compound. A selective phosphorylation of pyridinium nucleosides is very difficult. Either the introduction of protective groups or their removal afterward can pose problems. α-l-chloro-2,3,4-tri,-O-acetylglucopyranose has been used as the sugar compound to prepare the NMN analog nicotinamide-Nl-β- D -glucopyranosyl-6-phosphate. The free hydroxy group in the 6-position of this sugar allows the selective phosphorylation later on and the acetyl group in the cis-position to the halogen favors the formation of the β-anomer.

Gas-chromatographische Analyse freier aromatischer Mono-und Dicarbonsäuren

Gas chromatographic conditions are described which allow separation of free aromatic mono- and dicarboxylic acids. The new method provides better economy in routine analysis and avoids systematic errors due to uncontrolled chemical modifications of the substrate during introduction of protective groups.