Carboxylate moiety, reactive

High levels of regio- and stereoselectivity were observed in metal-catalyzed 1,3-DC of acyclic nitrones with a -hydroxy enones. The reaction probably occurs through the formation of reactive 1,4-metal-chelated intermediates. The remarkable diastereo- and enantiocontrol could be obtained through two complementary approaches by using a camphor-derived a -hydroxy enone in combination with Cu(OTf)2 or an achiral enone such as 81 in combination with the bis(oxazoline)-Cu(II) catalyst 83. At the end, the hydroxylated auxiUaiy could be easily removed. For example, treatment with periodic acid released a carboxylic moiety as in 86 and 87 <05AG(E)6187>. 

Model studies for metallo- 3-lactamases have been performed using mononuclear zinc hydroxide complexes.99,129,130 The breadth of (3-lactam hydrolysis reactivity of hydro-tris(pyrazolyl)borate-ligated mononuclear zinc hydroxide complexes has been explored.129 Treatment of the mononuclear zinc hydroxide complex [(Tpph Mc)Zn OH] with simple 3-lactams ( 3-propiolactam, 4-phenyl-(3-propiolactam, Scheme 21) does not result in ring opening, but instead results in the formation of 3-lactamide complexes and water. Treatment of [(Tpph,Me)Zn-OH] with /V-alkyl or -aryl 3-lactam derivatives instead results in no reaction (Scheme 21). Use of natural derivatives of penicillin and cephalosporin (Scheme 22) did not yield 3-lactam hydrolysis, but instead coordination of the carboxylate moiety of the antibiotic derivatives to the mononuclear Zn(II) center and release of water. 

The formation of guanidino side products is not critical for the stepwise solid-phase synthesis of standard peptides, in which a preactivation of reactive amino acids is conducted. However, if activation in situ is carried out or activation of hindered amino acids, protected peptides, or a carboxylic moiety before a cycli-zation step is performed, the use of phosphonium salts may be more efficient. For slow activation reactions, the addition of more coupling reagent (e.g., PyAOP) during the course of the reaction is advisable because the coupling derivative is hydrolyzed after a few minutes. 

Mixed anhydride method, a procedure of peptide coupling using reactive species resulting from the carboxylic moiety of a N-acylated amino acid and alkyl chlorocar-bonates (alkyl chloroformates), especially isobutyl chlorocarbonate (isobutyl chloro-formate), that readily reacts with an amino component. The nucleophilic amino component attacks the carboxy group of the amino acid component, with formation of the desired peptide derivative and release of the unstable isobutyl carbonic acid which immediately decomposes into carbon dioxide and isobutanol [J. Meienhofer, in The Peptides Analysis, Synthesis, Biology,... 

These radical species then induce chain scission, radical transfer, oxidation, and disproportionation to generate functional surface groups such as hydroxyl and carboxyl moieties (Fig. 1). For some materials, such as PDMS, these activated surfaces can be bonded to fabricate channels, as shown in Fig. 2. Plasma treatment of microchannels can also be used to control surface properties by incorporating reactive molecules or... 

Thus, while past experiments with sulfonate containing resins far outweighs past experiments employing carboxylate containing resins, the carboxylate moieties have been shown in the present study to be superior with respect to uranyl ion complexation when the particular reactive groups are contained in polymers or as difunctional monomers. 

The free carboxyl groups on the acrylic graft co-polymer can be neutralised with a tertiary amine which can activate an esterification reaction between the acrylic carboxyl moieties and the epoxy reactive sites. On the addition of de-ionised water, the free carboxyl moieties of the acrylic co-polymer react with the amine to produce a water soluble or dispersible quaternary ammonium hydrogel of the modified epoxy. 

As with other groups, halogens can substitute hydrogen in organic compounds containing additional functional moieties such as carboxylic acids to form acid chlorides, e.g. acetyl chloride CH3COCI. These are reactive acidic compounds liberating hydrochloric acid on contact with water. 

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