Cysteine formaldehyde derivative

The ring closure of L-cysteine by reaction with aldehydes or ketals 190 194 involving Schiff s base intermediates 195 leads to (4R)-thiazolidine-4-carboxylic acids. Except for formaldehyde and symmetrical ketones, the condensation of L-cysteine with aldehydes or unsymmetrical ketones generates a mixture of epimers, i.e. (25,4R)- and (2R,4R)-thiazolidine-4-carboxylic acid derivatives that can be separated by RP-HPLC or fractional crystallization. 139 ... 

Cysteine forms a similar derivative with formaldehyde, a process sometimes used in derivatization of cysteine. 

The transformations of the alkylating agent, methylene dimethane-suljdionate (MDS), were studied in rats and mice . Formaldehyde is formed metabolically from MDS and is incorporated into the methyl group of methionine. Other metabolites, derived from formaldehyde, are N-formyl cysteine and N,N -diformyl cystine. Methanesulphonic acid was identified as a metabolite of MDS in the mouse. 

Equilibrium constants for the reactions of cysteine derivatives with formaldehyde, and proton dissociation constants for the eight species of cysteine which exist in solution within the pH range 0—14, provide essential background information for evaluating the complex pH-rate profile for the formation of L-thiazolidine-4-carboxylic acid (18) from L-cysteine and formaldehyde. ... 

Proteins and their derivatives, especially the lectins, extracellular to the cell wall, are now a common observation (Tables 5.1.1 and 5.1.2). Lectins from the bark of black locust (Robinia pseudoacacia) have been isolated by specific absorption on formaldehyde-fixed human erythrocytes and eluted with a borate solution (68). The lectin is homogeneous on disc electrophoresis and yields three bands on isoelectric focusing. It has a molecular weight of s 110000 and consists of two subunits (MW 29000 and 31500). Its pi is 5.9 and it contains large amounts of aspartic acid, threonine, and serine, no cysteine, and very little methionine. Covalently bound neutral sugar constitutes 7.2% of the structure and glucosamine constitutes 0.47%. 

Ratner and Clarke [128] noted that the thiazolidine derived from cysteine and formaldehyde was quite stable to acid. The equilibrium could only be displaced toward the cleavage products by some irreversible process. Presumably the difference in behavior between the acetone and formaldehyde systems reflects the difference in stability of the intermediate cations, (57) (R = R = H R=R = CH3). Cleavage of the formaldehyde system presumably affords a less selective and... 

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