Amino acids alicyclic

A number of further transformations of homologous alicyclic amino acids to give various heterocycles have been performed [44,46,123-145]. 

The effect of C ,C -disubstituted amino acids (aaAAs) on peptide secondary structure has been studied in recent years.2a d While longer side-chain C ,C -di-n-alkyl amino acids promote extended peptide conformation,23 alicyclic aaAAs, in which the Ca carbon forms a cyclic bridge with itself, such a 1-aminocyclopentane-l-carboxylic acid (Ac5c) and 1-aminocyclohexane-l-carboxylic acid (Ac6c), have helix-forming characteristics similar to those of 1 -aminoisobutyric acid (Aib).2ax... 

Enolate additions to p-halovinyl sulfones (289a) show synthetic promise notable is the procedure, by Metcalf, for vinylation of a-amino acid derivatives, e.g. (289a — 317 — 318).220 Recently, Ban reported that alicyclic ketone enolates add to the acetyl cation equivalent (319) to afford 1,3-diketones (Scheme 98).22(" In general, (3-halovinyl sulfones are synthetically superior to the (3-halovinyl sulfoxides. 

In 2002, alicyclic cis-(3-amino acids have been reported to react with cyclohexyl isocyanide and substituted benzaldehyde via a liquid-phase Ugi four-center... 

A more direct method for the enantioselective ring opening of unactivated bicyclic /3-lactams has been reported. When lipolase (modified lipase B from Candida antarctica adsorbed on a macroporous resin) was allowed to interact with racemates 126 (n 1 or 2) and 127 (n= 1 or 2) in aqueous diisopropyl ether at 70 °C for 4.5-7 h, the products were the enantiomerically pure ring-opened unsaturated alicyclic /3-amino acids 128 (n = 1 or 2) and 129 (n 1 or 2), and the bicyclic /3-lactams 130 ( = 1 or 2) and 131 (n = 1 or 2) in 45 48% yield with ee 95-99% (Equations 13 and 14) <2004TA2875>. 

Conjugation has a great influence on the structure of aliphatic and alicyclic compounds. Thus, the existence of an amino form has been established (in addition to the extreme case of aromatic amines17) for all compounds where the double bond is conjugated with a carbonyl group (or its equivalent),12 with esters12,18 and nitriles of a,/8-un-saturated /8-amino acids,519,20 and with /8-amino-ketones. The /3-keto-esters ethyl 2-cyclopentanone- 1-carboxylate and ethyl 2-cyclo-hexanone-l-carboxylate exist as mixtures containing 95% of the keto... 

Alicyclic P-lactams 28 were successfully synthesized via a parallel liquid-phase Ugi four-center three-component reaction, starting from alicyclic P-amino acids such as cis-2-aminocyclohexanecarboxylic acid, c/.s-2-aminocyclopentanecarboxylic acid, 2,3-diexo-3-aminobicyclo-[2.2.1]heptane-2-carboxylic acid and some of their partially unsaturated analogues <02OL1967>. 

Gabapentin (= Neurontin 1 -Aminomethyl cyclohexane- carboxylic acid)] (amino alicyclic carboxylic acid) Synthetic GABAB-R agonist... 

Biotransformations of hve-membered alicyclic trani-A-protected-amino nitriles proceeded faster than in case of six-membered compounds. The products of the trani-A-protected-amino nitriles (amides and acids) were formed preferentially than the products of the c A-counterparts (only amides). Enantioselectivities were strongly dependent on the structure the trani-hve-membered substrates gave exclusively amides with excellent optical purity (94-99%), in contrast to the tran -six-membered substrates resulted in the formation of the acid with excellent enantiopurity (87-99%). The corresponding c A-compounds yielded much lower enantiomeric excesses. Nitrile precursor of a-methylene-P-amino acids was analogously investigated (Winkler et al., 2005) (Table 17.13). 

Alicyclic p-amino acids cis and irons 2-aminocyclohexane-1 -carboxylic acids and cis and trails 2-amino-4-cyclohexene-l-carboxylic acids crown-ether (Crownpak CR) [351... 

A broad variety of substrates were efficiently glycosylated by glycosidases such as aliphatic and alicyclic alcohols [14], phenols, oximes, steroids and terpenes [15], amino acids [16], alkaloids [17] and many other substances. 

In the phenylation reaction of substituted anilines, the electronic nature of the substituents plays a role only on the reaction rate, not on the overall yield (4-methoxyphenyl 91% after 15 minutes and 4-nitrophenyl 90% after 16 hours). The steric hindrance is also a factor which influences the reaction in slowing down the reaction rate. To obtain good to excellent yields, an excess of bismuth reagent is then required with hindered substrates. For example, mesitylamine required 2.2 equivalents of triphenylbismuth diacetate to afford the AT-phenyl derivative in 92% after 24 hours. Moreover, triphenylamine was obtained in 23% yield after 48 hours by arylation of, iV-diphenylamine. A variety of aliphatic, alicyclic, heterocyclic and aromatic amines as well as hydrazines were N-arylated by this system. No reaction took place with a-amino acids but their esters were mono-iV-phenylated under... 

Nicotine and related tobacco alkaloids produce their effects in biological systems by reacting at nicotinic acetylcholine receptors via the protonated N -alicyclic amino functional group. Compounds which are active tend to predominantly exist in the ionised form at physiological pH 7.4, whereas inactive compounds, such as cotinine, are virtually tmionised under these conditions. Unionised nicotine can pass freely across biological membranes in contrast to the ionised form where membrane transfer is greatly inhibited so that whilst nicotine is readily absorbed via the buccal cavity and intestine it is poorly absorbed from the acid environment of the stomach. 

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