5- Alkylcysteine derivatives

Amino acids Amines, methylated amino acids, betaines, cyanogenic glycosides, mustard oils, alkaloids, glycine conjugates, glutamine and ornithine, 5-alkylcysteine derivatives, di-oxopiperazines, peptides (penicillins), hydroxamic acids. 

The group of Park and Jew developed the efficient reaction systems for the preparation of optically active a-alkylserine and a-alkylcysteine derivatives (Scheme 6.15) [40], The group developed the oxazoline-based substrate for serines 52a and the thiazoline-based substrate 52b for cysteines, respectively. The oxazoline and thiazoline moieties fulfilled a dual function the activation of the a-proton and the protection of both the amino and the side chain hydroxy groups. The ortho-biphenyl derivatives 52a and 52b were specifically designed for the cinchona PTC 54, and solid cesium hydroxide monohydrate was chosen as an optimal base. The PTC 29 was also found to be as effective as the PTC 54 for the asymmetric alkylation of 52a. 

The enzyme resembled methionine 7-lyase in requiring pyridoxal phosphate for activity but it did not attack methionine. The engine was described as an S-alkylcysteinase because it used a range of S-alkylcysteines and S-alkylcysteinesulfoxides as substrates. Similar rates of attack were obtained with methylated and ethylated substrates whereas with propyl, butyl, isobutyl, allyl, amyl and isoamyl derivatives of cysteine the rates were between 40% and 75% lower. 

S-Alkylcysteine C-S Lyase (EC 4.4.1.6). The endosperm of seeds of the shrub Albizzia lophanta contains djenkolic acid (HOOCCH(NH2)-CH2SCH2SCH2CH(NH2)C00H) and an enzyme which cleaves it to pyruvate, ammonia, and highly odoriferous substances (CH2(SH)2 ) (48, 49). The enzyme has been purified 200-fold by acid and heat treatment, (NH4)2S04 precipitation, and adsorption on alumina (50). It has a broad specificity and cleaves S-derivatives of L-cysteine, its sulfoxide, and sulfone. L-Cysteine itself is cleaved to pyruvate, HjS, and ammonia. 

The chiroptical properties of a number of sulfur-containing amino acids (cysteine or cystine derivatives, such as lanthionine, cystathionine, allo-cystathionine, djenkolic acid, felinine, and S-alkylcysteines) have been described (Coleman and Blout, 1968 Casey and Martin, 1972 Jung et aL, 1973 Takagi et al, 1973 Ottnad et ai, 1975) and correlated with the chiroptical characteristics of the parent compounds. 

Other examples of shown effectiveness of PTCs were reported by Park, Jew, and co-workers [98], They developed enantioselective synthetic method for the preparation of (/ )-a-alkylserines and (S)-a-alkylserines based on asymmetric alkylation of phenyl or o-biphenyl oxazoUne derivatives using CBPTC XXXXVIa and binaphthol-derived Maruoka s catalyst XXV, respectively (Scheme 8.16). The same authors [99] also expanded this methodology to enantioselective synthesis of (/ )-a-alkylcysteines and (5)-a-alkylcysteines using thiazoline-4-carboxylates in PTC alkylation. In 2006, Maruoka and co-workers [100] reported first example of the catalytic asymmetric alkylation of glycolates that establishes stereogenic quaternary carbon centers (Scheme 8.17). Their approach utilized 3,5-diaryloxazolidin-2,4-diones 48 as novel... 

HgO 340), iron salts 28) or dicyclohexylcarbodiimide 205). Reactions of S-alkyl- or S-acylcysteine derivatives in basic media are often accompanied by P-elimination side reactions 180, 245, 246, 302). Elimination is favoured in polar solvents and is also dependent on the C -H acidity of the substrate. Accordingly, esters of S-alkylcysteines undergo elimination more readily than derivatives of other types. 

---