Amides centers

All studied model compounds can distinctly be divided into three groups (Table VII). The first group is composed of substances in which the sulfur, selenium or cyclopentadienyl anion acts as an anionic center. They exist only in open betaine forms, and their PES do not contain local minima corresponding to cyclic isomers. The second group contains compounds with arsonium cationic and oxide anionic centers and silicon and germanium betaines with arsonium and amide centers. They exist as cyclic isomers and their PES have no local minima corresponding to the open forms. Finally, the third group consists of six studied compounds with phosphonium cationic and oxide or amide anionic centers and arsonium-imide betaine. Their PES have minima for both cyclic and open forms separated by low barriers. 

The mercury-induced cyclization of amidals in which a stereogenic center is positioned at the amidal center adjacent to the nucleophilic amide functionality, gave oxazolidines with high stereoselectivity. Reaction of the amidals 10 with mercury(ll) acetate/mercury(ll) trifluoroac-etate in acetonitrile in the presence of sodium hydrogen carbonate followed by reductive cleavage with sodium borohydride afforded the corresponding fused oxazolidines 11164. 

Aluminum chloride [7446-70-0] is a useful catalyst in the reaction of aromatic amines with ethyleneknine (76). SoHd catalysts promote the reaction of ethyleneknine with ammonia in the gas phase to give ethylenediamine (77). Not only ammonia and amines, but also hydrazine [302-01-2] (78), hydrazoic acid [7782-79-8] (79—82), alkyl azidoformates (83), and acid amides, eg, sulfonamides (84) or 2,4-dioxopyrimidines (85), have been used as ring-opening reagents for ethyleneknine with nitrogen being the nucleophilic center (1). The 2-oxopiperazine skeleton has been synthesized from a-amino acid esters and ethyleneknine (86—89). 

The unexpected biological activities of tetracyclines, such as 5a-epi-6-epitetracychne [19543-88-5] C22H24N20g, and 7-chloro-5a,lla-dehydro-6-epitetracycline [22688-60-4] C22H22ClN20g, make predicting stmcture-activity relationships difficult (64). Aside from the C-2 amide Mannich-base derivatives, variation at other centers in the molecule, ie, C-4, 4a, 5a, 12a, decreases the biological activity. 

Appllca.tlons. MCA is used for the resolution of many classes of chiral dmgs. Polar compounds such as amines, amides, imides, esters, and ketones can be resolved (34). A phenyl or a cycloalkyl group near the chiral center seems to improve chiral selectivity. Nonpolar racemates have also been resolved, but charged or dissociating compounds are not retained on MCA. Mobile phases used with MCA columns include ethanol and methanol. 

The only sequence-specific hydrogen bonds between TBP side chains and the bases in the minor groove occur at the very center of the TATA box (Figure 9.7). The amide groups of two asparagine side chains donate four hydrogen bonds, two each to adjacent bases on the same DNA strand (Asn 69... 

A dry 1-1. three-necked round-bottomed flask is fitted in the center neck with a sweep-blade stirrer whose shaft passes through an airtight bearing (Note 1). One side neck is fitted with a condenser topped by a soda-lime drying tube, and the other is fitted with a solid stopper. In the flask are placed 75 ml. of piperidine (Note 2) and 15.6 g. (0.4 mole) of sodium amide (Note 3), and the mixture is heated at reflux (Note 4) for 15 minutes with good stirring. The mixture is cooled just below reflux temperature, and 46 g. (0.2 mole) of sodium -naphtha-lenesulfonate (Note 5) is added, followed by an additional 75 ml. of piperidine. The mixture is then heated at reflux for 12 hours with stirring. 

The [2 + 2] cycloaddition reaction of A -benzyl-l,4-dihydropyridine 34b with acrylonitrile, followed by catalytic reduction gave two pairs of diastereoisomeric amides 36 and 37 with a low diastereomeric excess, probably due to the large distance between the asymmetric center and the site of acrylonitrile attack. Compounds 36 and 37 were resolved into the four individual diastereoisomers (ca 5% for compound 36 and 15% for 37) [97JCR(M)321], Irradiation of 1,4-dibenzyl-1,4,5,6-tetrahydropyridine 38 in the presence of 29 gave two stereoisomers. 

An aryl alkyl ketone 1 can be converted into an tn-arylalkane carboxylic amide 2 by employing the Willgerodt reaction The number of carbon centers is retained. The reaction is carried out by treating the ketone with an aqueous solution of ammonium polysulfide. A variant that has been developed by Kindler, and which is called the Willgerodt-Kindler reaction, uses a mixture of sulfur and a secondary amine instead of the ammonium polysulfide. 

It seems reasonable that an enzyme which used poraaminobenzoic acid as a substrate might be deceived by sulfanilamide. The two compounds are very similar in size and shape and in many chemical properties. To explain the success of sulfanilamide, it is proposed that the amide can form an enzyme-substrate complex that uses up the active centers normally occupied by the natural substrate. 

A sequence of straightforward functional group interconversions leads from 17 back to compound 20 via 18 and 19. In the synthetic direction, a base-induced intramolecular Michael addition reaction could create a new six-membered ring and two stereogenic centers. The transformation of intermediate 20 to 19 would likely be stereoselective substrate structural features inherent in 20 should control the stereochemical course of the intramolecular Michael addition reaction. Retrosynthetic disassembly of 20 by cleavage of the indicated bond provides precursors 21 and 22. In the forward sense, acylation of the nitrogen atom in 22 with the acid chloride 21 could afford amide 20. 

When a cold (-78 °C) solution of the lithium enolate derived from amide 6 is treated successively with a,/ -unsaturated ester 7 and homogeranyl iodide 8, intermediate 9 is produced in 87% yield (see Scheme 2). All of the carbon atoms that will constitute the complex pentacyclic framework of 1 are introduced in this one-pot operation. After some careful experimentation, a three-step reaction sequence was found to be necessary to accomplish the conversion of both the amide and methyl ester functions to aldehyde groups. Thus, a complete reduction of the methyl ester with diisobutylalu-minum hydride (Dibal-H) furnishes hydroxy amide 10 which is then hydrolyzed with potassium hydroxide in aqueous ethanol. After acidification of the saponification mixture, a 1 1 mixture of diastereomeric 5-lactones 11 is obtained in quantitative yield. Under the harsh conditions required to achieve the hydrolysis of the amide in 10, the stereogenic center bearing the benzyloxypropyl side chain epimerized. Nevertheless, this seemingly unfortunate circumstance is ultimately of no consequence because this carbon will eventually become part of the planar azadiene. 

The original procedure for the trifluoroacetylation of amino acids used trifluoroacetic anhydride [Acetic acid, trifluoro-, anhydride].4 This reagent, although inexpensive and readily available, has certain disadvantages it is a highly reactive compound and thus has caused undesired reactions such as the cleavage of amide or peptide bonds,5 unsymmetrical anhydrides are formed between the newly formed A-trifluoroacetylamino acids and the by-product trifluoroacetic acid, and excess trifluoroacetic anhydride has caused racemization of asymmetric centers. 

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