Acids, aliphatic imino

Except for the abnormally low yield with lactim ethers derived from 3-carbethoxylactams with amidines depends on the stability of the reagents.120 Lactim ethers, just as aliphatic imino ethers, are labile to acidic and alkaline media, hence the yields depend on the rate of cyclization. With basic or enolizable amidines, the... 

Amino groups are considerably less acidic than hydroxyl groups, and in aliphatic chemistry imino compounds are generally far less... 

While screening for p-lactam antibiotics stable to p-lactamases, a strain of Streptomyces lactamdurans was found to contain several such agents which have a 6-a-methoxy group whose electronic and steric properties protect the antibiotic from enzymatic attack. Cephamycin C (29a), one of these substances, is not of commercial value, but side chain exchange has led to much more potent materials. Of the various ways of effecting this transformation, one of the more direct is to react cephamycin C with nitrous acid so that the aliphatic diazo product (29b) decomposes by secondary amide participation giving cyclic iminoether 30. The imino ether moiety solvolyzes more readily than the p-lactam to produce 7-aminocephamycinic... 

Ligand-free catalysts have been prepared from the following types of nickel(II) compounds nickel salts of long-chain aliphatic or aromatic carboxylic acids (10, 11) or of sulfonic acids (11), nickel enolates of /3-diketones (11) [e.g., nickel acetylacetonate (4, 12)] or their imino derivatives (11, 13), nickel phenolates (11), dithiocarbamates (14), and mer-captides (15). 

An enantioselective imino-ene reaction was developed by Lectka to provide ct-amino acid derivatives.27 Aryl alkenes (cr-methyl styrene, tetralene), aliphatic alkenes (methylene cyclohexane), and heteroatom-containing enes, all gave high yields and high ee s of the homoallylic amides (Equation (17)). The mechanism of this reaction has been proposed to proceed through a concerted pathway. This mechanism is evidenced by a large kinetic isotope effect observed in the transfer of H(D). 

Based on the properties of the side chains, the 20 amino acids can be put into six general classes. The first class contains amino acids whose side chains are aliphatic, and is usually considered to include glycine, alanine, valine, leucine, and isoleucine. The second class is composed of the amino acids with polar, nonionic side chains, and includes serine, threonine, cysteine, and methionine. The cyclic amino acid proline (actually, an imino acid) constitutes a third class by itself. The fourth class contains amino acids with aromatic side chains tyrosine, phenylalanine, and tryptophan. The fifth class has basic groups on the side chains and is made up of the three amino acids lysine, arginine, and histidine. The sixth class is composed of the acidic amino acids and their amides aspartate and asparagine, and glutamate and glutamine. 

Replacement of carbon atoms in the cyclic aliphatic side chain of proline with nitrogen leads to the azaprolines where incorporation of an additional imino group may affect molecular recognition processes via electrostatic interactions. While the proline analogues imidazoli-dine-2-carboxylic acid (3-azaproline, 15) and pyrazolidine-3-carboxylic acid (5-azaproline, 16) allow for additional side-chain modifications in peptidomimetic structures, with pyr-azolidine-2-carboxylic acid (2-azaproline, 17) (Table 2), where the a-CH is replaced by nitrogen, the peptide backbone is modified with consequently strong conformational effects. 

Among the reactive groups in wool the most important are amino, imino, and hydroxyl groups. Reactions occur in a weakly acidic medium (pH 3-5) and include nucleophilic substitution of leaving groups (usually Cl, F, and, rarely, sulfonate or ammonium groups) or addition reactions to polar aliphatic double bonds. 

This reaction is known as the Pinner synthesis. The salt formed may be converted to the free imino ester by treatment with a weak base. It may also be converted to the corresponding ester by an aqueous acid catalyzed hydrolysis. The Pinner reaction is of a general nature and is applicable to aliphatic, aromatic and heterocyclic alcohols. 

Similarly, urea TV, 0-acetal 64 undergoes condensation reaction with weak carbon acids to afford acyclic 1,1-enediamines with the elimination of alcohol and amine42,95. A number of active methyl compounds such as an aliphatic ketone, acetophenone, imino ester and thioacetoamide has been successfully converted to 1,1-enediamines. Lactones, lactams and thiolactams condense with 64 to give enediamines 65 in moderate yields (equation 24). Very weakly activated methyl groups are also reactive towards urea A, 0-acetal 64, and 1,1-enediamines 66-71 are prepared from the corresponding reactants42,95. 

Nitriles are directly converted to esters by heating with an alcohol and sulfuric or hydrochloric acid. When water is absent, the imino ester salt is readily isolated (method 402). Aliphatic,aromatic, and heterocycliccyano compounds react in this manner. Most of the aromatic compounds contain a cyanomethyl group although the cyanide radical may be attached directly to the aromatic nucleus. Monosub-stituted malonic esters free from unsubstituted and disubstituted malonic esters are made from the corresponding a-cyano esters by this method. Malonic ester and disubstituted malonic esters have been similarly prepared. ... 

Amino-3-pyrazolin-5-ones (4-imino-3-pyrazolidinones) react with nitrous acid as do ordinary aromatic amines to form diazonium salts.426,984,1353 These then couple readily with aromatic amines,1017,1018,1060 phenols992,1323 and aliphatic compounds having active hydrogen atoms,428,1017 such as acetoacetic esters. The products are 4-azo-3-pyrazolin-5-ones (eq. 200). The diazonium salts also couple... 

In compounds which have no substituents at N-l or N-2 nuclear acylation also occurs and under some conditions acylation occurs at C-4. The use of 2-alkyl- or aryl-5-imino-3-pyrazolidinones, which exist as the 3-amino-2-pyrazolin-5-one isomer, with an equivalent of acid chloride, either aliphatic or aryl, leads to 3-acylamides (eq. 266),14,67,594,695,1247,1594,1595 although in some cases a side-reaction gives both N- and O-acylation.1595 Under the same conditions 3-hydroxy-5-imino-2-pyrazolinones give O-acylation.1599 The reaction of... 

The ninhydrin reaction is not restricted to a-amino acids, however. It is well known that imino acids, notably proline, but also for example pipecolic acid, in solution produce a different color with an absorption maximum at 440 nm. Primary aliphatic amines react likewise with ninhydrin to give Ruhe-man s purple but the color yield is lower than for a-amino acids. Peptides, amino acids with secondary amino groups, mainly N-methylamino acids, and secondary amines also react with ninhydrin, although often more slowly and with smaller yield than the a-amino acids. Tertiary amines and all aromatic amines do not react with ninhydrin. Ammonia itself reacts to give a color with ninhydrin, although with a rather low yield. 

---