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2-azetidinone
A beta-lactam (β-lactam) ring is a four-membered lactam. A ''lactam'' is a cyclic amide, and ''beta''-lactams are named so because the nitrogen atom is attached to the β-carbon atom relative to the carbonyl. The simplest β-lactam possible is 2-azetidinone. β-lactams are significant structural units of medicines as manifested in many β-lactam antibiotics Up to 1970, most β-lactam research was concerned with the penicillin and cephalosporin groups, but since then, a wide variety of structures have been described. Clinical significance The β-lactam ring is part of the core structure of several antibiotic families, the principal ones being the penicillins, cephalosporins, carbapenems, and monobactams, which are, therefore, also called β-lactam antibiotics. Nearly all of these antibiotics work by inhibiting bacterial cell wall biosynthesis. This has a lethal effect on bacteria, although any given bacteria population will typically contain a subgroup that is resistant to Π... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta-lactam
A beta-lactam (β-lactam) ring is a four-membered lactam. A ''lactam'' is a cyclic amide, and ''beta''-lactams are named so because the nitrogen atom is attached to the β-carbon atom relative to the carbonyl. The simplest β-lactam possible is 2-azetidinone. β-lactams are significant structural units of medicines as manifested in many β-lactam antibiotics Up to 1970, most β-lactam research was concerned with the penicillin and cephalosporin groups, but since then, a wide variety of structures have been described. Clinical significance The β-lactam ring is part of the core structure of several antibiotic families, the principal ones being the penicillins, cephalosporins, carbapenems, and monobactams, which are, therefore, also called β-lactam antibiotics. Nearly all of these antibiotics work by inhibiting bacterial cell wall biosynthesis. This has a lethal effect on bacteria, although any given bacteria population will typically contain a subgroup that is resistant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2-azetidinone
A beta-lactam (β-lactam) ring is a four-membered lactam. A ''lactam'' is a cyclic amide, and ''beta''-lactams are named so because the nitrogen atom is attached to the β-carbon atom relative to the carbonyl. The simplest β-lactam possible is 2-azetidinone. β-lactams are significant structural units of medicines as manifested in many β-lactam antibiotics Up to 1970, most β-lactam research was concerned with the penicillin and cephalosporin groups, but since then, a wide variety of structures have been described. Clinical significance The β-lactam ring is part of the core structure of several antibiotic families, the principal ones being the penicillins, cephalosporins, carbapenems, and monobactams, which are, therefore, also called β-lactam antibiotics. Nearly all of these antibiotics work by inhibiting bacterial cell wall biosynthesis. This has a lethal effect on bacteria, although any given bacteria population will typically contain a subgroup that is resistant to Π... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cholesterol Absorption Inhibitor
Cholesterol absorption inhibitors are a class of compounds that prevent the uptake of cholesterol from the small intestine into the circulatory system. Most of these molecules are monobactams but show no antibiotic activity. An example is ezetimibe (SCH 58235) Another example is Sch-48461. The "Sch" is for Schering-Plough, where these compounds were developed. Phytosterols are also cholesterol absorption inhibitors. Physiology There are two sources of cholesterol in the upper intestine: dietary (from food) and biliary (from bile). Dietary cholesterol, in the form of lipid emulsions, combines with bile salts, to form bile salt micelles from which cholesterol can then be absorbed by the intestinal enterocyte. Once absorbed by the enterocyte, cholesterol is reassembled into intestinal lipoproteins called chylomicrons. These chylomicrons are then secreted into the lymphatics and circulated to the liver. These cholesterol particles are then secreted by the liver into the blood as VLD ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Penicillin Binding Proteins
Penicillin-binding proteins (PBPs) are a group of proteins that are characterized by their affinity for and binding of penicillin. They are a normal constituent of many bacteria; the name just reflects the way by which the protein was discovered. All β-lactam antibiotics (except for tabtoxinine-β-lactam, which inhibits glutamine synthetase) bind to PBPs, which are essential for bacterial cell wall synthesis. PBPs are members of a subgroup of enzymes called transpeptidases. Specifically, PBPs are DD-transpeptidases. Diversity There are a large number of PBPs, usually several in each organism, and they are found as both membrane-bound and cytoplasmic proteins. For example, Spratt (1977) reports that six different PBPs are routinely detected in all strains of ''E. coli'' ranging in molecular weight from 40,000 to 91,000. The different PBPs occur in different numbers per cell and have varied affinities for penicillin. The PBPs are usually broadly classified into high-molecular ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mukaiyama's Reagent
was a Japanese organic chemist. One of the most prolific chemists of the 20th century in the field of organic synthesis, Mukaiyama helped establish the field of organic chemistry in Japan after World War II. Education Mukaiyama studied chemistry at the Tokyo Institute of Technology, earning his BSc in synthetic organic chemistry in 1948. He became assistant professor at Gakushuin University in 1953, where he stayed until he received his Ph.D. in synthetic organic chemistry from the University of Tokyo in 1957. Research and career Early work Mukaiyama became an assistant professor at the Tokyo Institute of Technology in 1958 and earned his full professorship in 1963. During this time, his main focus was on organophosphorus chemistry. While examining deoxygenation reactions involving phosphines, Mukaiyama found that the mercury(II) acetate employed as a catalyst would react with phosphorus(III) compounds to produce acetic anhydride. This initial example expanded into the concept o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grignard Reagent
A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . They are a subclass of the organomagnesium compounds. Grignard compounds are popular reagents in organic synthesis for creating new carbon-carbon bonds. For example, when reacted with another halogenated compound in the presence of a suitable catalyst, they typically yield and the magnesium halide as a byproduct; and the latter is insoluble in the solvents normally used. In this aspect, they are similar to organolithium reagents. Pure Grignard reagents are extremely reactive solids. They are normally handled as solutions in solvents such as diethyl ether or tetrahydrofuran; which are relatively stable as long as water is excluded. In such a medium, a Grignard reagent is invariably present as a complex with the magnesium atom conn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenyl Group
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen, which may be replaced by some other element or compound to serve as a functional group. Phenyl group has six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the remaining carbon bonded to a substituent. Phenyl groups are commonplace in organic chemistry. Although often depicted with alternating double and single bonds, phenyl group is chemically aromatic and has equal bond lengths between carbon atoms in the ring. Nomenclature Usually, a "phenyl group" is synonymous with C6H5− and is represented by the symbol Ph or, archaically, Φ. Benzene is sometimes denoted as PhH. Phenyl groups are generally attached to other atoms or groups. For example, triphenylmethane (Ph3 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more Unsaturated hydrocarbon, unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the Multiplicity (chemistry)#Molecules, bond multiplicity". The resulting reaction is a cyclization reaction. Many but not all cycloadditions are Concerted reaction, concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic. As a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile. Cycloadditions can be described using two systems of notation. An older but still common notation is based on the size of linear arrangements of atoms in the reactants. It uses parentheses: where the variables are the numbers of linear atoms in each reactant. The product is a cycle of size . In this system, the standard Diels-Alder reaction is a (4 + 2)-cyc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diphenylketene
Diphenylketene is a chemical substance of the ketene family. Diphenylketene, like most disubstituted ketenes, is a red-orange oil at room temperature and pressure. Due to the successive double bonds in the ketene structure R1R2C=C=O, diphenyl ketene is a heterocumule. The most important reaction of diphenyl ketene is the +2cycloaddition at C-C, C-N, C-O, and C-S multiple bonds. History Diphenyl ketene was first isolated by Hermann Staudinger in 1905 and identified as the first example of the exceptionally reactive class of ketenes with the general formula R1R2C=C=O (R1=R2=phenyl group). Preparation The first synthesis by H. Staudinger was based on 2-chlorodiphenylacetyl chloride (prepared from benzilic acid and thionyl chloride) from which two chlorine atoms are cleaved with zinc in a dehalogenation reaction: An early synthesis uses benzilmonohydrazone (from Diphenylethanedione and hydrazine hydrate), which is oxidized with mercury(II)oxide and calcium sulfate to form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzaldehyde
Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. The primary component of bitter almond oil, benzaldehyde can be extracted from a number of other natural sources. Synthetic benzaldehyde is the flavoring agent in imitation almond extract, which is used to flavor cakes and other baked goods. History Benzaldehyde was first extracted in 1803 by the French pharmacist Martrès. His experiments focused on elucidating the nature of amygdalin, the poisonous material found in bitter almonds, the fruit of ''Prunus dulcis''. Further work on the oil by Pierre Robiquet and Antoine Boutron-Charlard, two French chemists, produced benzaldehyde. In 1832, Friedrich Wöhler and Justus von Liebig first synthesized benzaldehyde. Production As of 1999, 7000 tonnes of synthetic and 100 tonnes of natural b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
