Schiffbase amines

Schiffbase, 1147 Scurvy vitamin C and, 772 sec-Butyl group, 84 Second-order reaction, 363 Secondary alcohol, 600 Secondary amine, 917 Secondary carbon, 84 Secondary hydrogen. 85 Secondary structure (protein), 1038-1039... 

Formation of /1-lactams by the reaction of an acid chloride, a SchifFbase and a tertiary amine (Eq. 62) appears to involve multiple pathways, some of which are very fast at higher temperatures. When conducted in open vessels in unmodified micro-wave ovens, high level irradiation leads to preferential formation of the trans -lactams (55%) whereas, at low power, the cis isomer was obtained as the only product (84%). The failure of the cis isomer to isomerize to the trans compounds is an example of induced selectivity. 

A simple, fast and specific color test for urea nitrate was reported recently by Almog et al. It is based on the reaction between urea nitrate and ethanolic solution ofp-dimethylaminocinnamaldehyde (p-DMAC) (9) under neutral conditions [91]. A red pigment is formed within 1 min from contact. Its structure has also been determined by the same group, by X-ray crystallography [92]. It appears to be a resonance hybrid between a protonated Schiffbase (10) and a quinoid system (10a) (Eq. (14)). The limit of detection on filter paper is 0.1 mg/cm. Urea itself, which is the starting material for urea nitrate, does not react with p-DMAC under the same conditions. Other potential sources of false-positive response such as common fertilizers, medications containing the urea moiety and various amines, do not produce the red pigment with p-DMAC. 

Soloshonok and co-workers have developed a method for the synthesis of a-(perfluoro-alkyl)amines from perfluoroalkyl carbonyl compounds by a transamination involving an azomethine a/omethine (Schiffbase) isomerization. They call this method a biomimetic, base-catalyzed 1,3-proton shift reaction, and have applied it to perfluoroaldehydes,12-15 perfluoroalkyl ketones,12 18 / -(perfluoroalkyl)-/l-oxo esters,15 16 19 24 and - -( perfluoroalkyl)-a-oxo es-ters2 " -26 to synthesize the corresponding a-(perfluoroalkyl)amincs, / -(perfluoroalkyl )-/i-amino acids, and 3 -(perfluoroalkyl)- x-amino acids. 

Schiffbase formation followed, by reduction a cis-trans isomerization is necessary to suitably position the amine and aldehyde groups... 

Although the Schiffbase (pyrol)3tren) (17) formed by condensation of pyrrole-2-carboxaldehyde with 2,2, 2"-tris(ethylamino)amine is potentially heptadentate the neutral low-spin complex [Fe (py-rol)3 tren ] has a six-coordinate (trigonally distorted octahedral) structure, the distance between the metal atom and the central tertiary aliphatic nitrogen being greater than the van der Waals contact... 

Formation of this carbinolamine bond is revealed by the continuous electron density that connects the aldehyde group of the antibiotic to Hm A2103 in the unbiased electron density maps obtained for each of the 16-membered macrolides studied to date, each of which has an aldehyde group extending from C6. Not surprisingly, that continuous electron density feature is absent in the unbiased electron density map calculated for the structure of the 15-membered macrolide azithromycin which has no aldehyde group at C6. The electron density feature is consistent with formation of a carbinolamine bond and not with a SchifFbase, consistent with the expected chemical reactivity between exocyclic amines and aldehydes (Fig. 4.9) [21]. 

The crystal stmctures of snbstrate-rednced amine oxidases have been solved, along with site-directed mutants, metal-snbstitnted forms, enzyme complexes with inhibitors, the Oi mimic nitric oxide (NQ) and peroxide. These have been correlated with a wealth of biochemical and spectroscopic data that form the basis for the catalytic mechanism proposed in Scheme 8. A Schiffbase complex species (b) is formed between snbstrate amine and TPQ C-5. Base-catalyzed proton abstraction from substrate a-methylene group, via the conserved active-site aspartate residue, yields the reduced cofactor in a product Schiff-base complex, species (c). Hydrolysis releases product aldehyde, leaving the cofactor in the reduced aminoquinol form, species (d). 

Hydroamination reactions involving alkynes and enantiomerically pure chiral amines can produce novel chiral amine moieties after single pot reduction of the Schiffbase intermediate 82 (Scheme 11.27) [123]. Unfortunately, partial racemiza tion ofthe amine stereocenter was observed with many titanium based hydroamina tion catalysts, even in the absence of an alkyne substrate. No racemization was observed when the sterically hindered Cp 2TiMe2 or the constrained geometry catalyst Me2Si(C5Me4)(tBuN)Ti(NMe2)2 was used in the catalytic reaction. Also, the addition of pyridine suppressed the racemization mostly. 

Starting from 2-(benzyloxycarbonyl)amino-2-deoxy-D-glucose and potassium di-tert-butyl oxalacetate,195 N-(benzyloxycarbonyl)neur-aminic lactone (66, R = —COO—CH2Ph) was obtained. Hydro-genolysis of the benzyloxcarbonyl group led to free neuraminic acid, which forms a pH-dependent equilibrium mixture of the free base (67) and its internal Schiffbase (68). 

The stoichiometry of the reductive half-reaction is shown in Equation (2). The initial step in this reaction, as depicted in Figure 13, involves the nucleophilic attack of the primary amine substrate at C5 of oxidized TPQ (Figures 13(a) —> 13(b)). This results in the formation of a substrate Schiffbase (Figure 13(b)). In the next step, an active site base (a conserved aspartic acid) abstracts a proton to form a carbanion species (Figure 13(c)), which quickly rearranges to form a product Schiffbase (Figure 13(d)). The product aldehyde is formed by... 

The only jU-superoxo complexes to have been characterized are those which contain cobalt. They are readily prepared by treatment of the corresponding /i-peroxo complexes with strong oxidants. Thompson and Wilmarth observed that MnO, HOCl, Br2, BrOf and NOf are all effective oxidants toward [(en) Co(/r-NH2,02)Co(en)2] in acidic solution whereas Fe ", HjOj, Ag" " and CtjO are not. In other systems CI2, Pb02, persulfate and Ce in nitric acid solution have also effected oxidation. A number of well-characterized //-superoxo cobalt(III) complexes are listed in Table 55. There are no reports of /i-superoxo complexes containing Schiffbase ligands and all that are known contain either terminal amine or cyano groups. 

Mannich reaction A reaction in which a primary or secondary amine reacts with methanal (formaldehyde) and a carbonyl compound to produce an amino-carbonyl compoimd. It takes place in two stages. First the amine reacts wiA methanol to form a Schiffbase ... 

Some examples of DKR based on racemization of secondary alkyl amine via Shiff base were shown in Scheme 5.9. Schiffbase formation of a-amino carboxylic esters significantly increases the acidity of the a-proton in comparison to that of the parent amino acid, thus enabling enantiomer-selective hydrolysis and ammonoly-sis through DKR [23]. For example, chymotrypsin catalyses the hydrolysis of a Schiff base of phenylalanine ethyl ester and an aromatic aldehyde (Scheme 5.9, Equation 5.6) [23b]. In this particular case, natural phenylalanine precipitates, leaving the aldehyde and unhydrolysed enantiomeric ester in solution. Addition of l,4-diazabicyclo[2.2.2]octane (DABCO) (as the Bronsted base) allows DKR to take place by promoting racemization of the Schiffbase. Similarly, Novozym 435... 

Schiffbase A class of derivatives of the condensation of aldehydes or ketones with primary amines... 

SchiffBase lshifs- A reaction intermediate compound characteristic of reactions involving amines in general formula is RNH-CO-N = CH2 often used in formation of ureaformaldehyde polymers. (Smith MB, March J (2001) Advanced organic chemistry, 5th edn. Wiley,... 

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