Protection choline esters

Enzyme Labile Carboxyl Protecting Groups Choline Ester (OCho)... 

Scheme 9. N-Ras peptide synthesis employing choline esters as C-terminal protecting group. EDC 1-ethyl-3 (dimethylamino)propyl-carbodiimide hydrochloride, HOBt 1-hydroxybenzo-tri azole...

Peptide 21, synthesized using the C-terminal enzymatic-cleavable choline ester (Scheme 11), was also synthesized using the C-terminal allyl ester protecting group (Scheme 12). The selective Pd(0)-catalyzed... 

Schelhaas M, Glomsda S, Hansler M, Jakubke HD, Waldmann H. Enzymatic synthesis of peptides and Ras lipopeptides employing choline ester as a solubilizing, protecting, and activating group. Angew. Chem. Int. Ed. 1996 35 106-109. 

The solubilizing capacity of the choline residue is so pronounced that even substrates combining two hydrophobic amino acids are homogeneously soluble in aqueous buffer without any additional cosolvent. These favorable physical properties were also used in the enzymatic formation of peptide bonds. The amino acid choline ester 38 acts as the carboxyl component in kinetically controlled peptide syntheses with the amino acid amides 39 and 40 [52] (Fig. 11). The fully protected peptides 41 and 42 were built up by means of chymotrypsin in good yields. Other proteases like papain accept choline esters as substrates also, and even butyrylcholine esterase itself is able to generate peptides from these electrophiles. 

Sinapoyl esters are phenolic compounds found in members of the Brassicaceae, which includes the model plant Arabidopsis thaliana. The two major sinapoyl esters are sinapoyl malate (3.92) and sinapoyl choline (3.93), which accumulate in leaves and seeds, respectively. Sinapoylmalate plays a role in the protection against UV-radiation (Landry et al., 1995), whereas sinapoyl choline may be used as a storage form of choline in seeds (Shirley and Chappie, 2003). The precursor of these two esters is sinapate (3.35). 

Choline nitrite, or pseudo-muscarine, was at one time thought to be identical with natural muscarine, the highly poisonous alkaloid of the mushroom Amanita muscaria (Fly Agaric), and to be the aldehyde corresponding to choline. Both suppositions are wrong. The natural alkaloid is much more toxic than choline nitrite, and its effects are antagonised by atropine, which has little protective effect against the synthetic ester. 

In a sphingomyelin, the amine group of sphingosine forms an amide bond to a fatty acid and the hydroxyl group forms an ester bond with phosphate, which forms another phos-phoester bond to choline or ethanolamine. The sphingomyelins are abundant in the white matter of the myelin sheath, a coating surrounding the nerve cells that inCTeases the speed of nerve impulses and insulates and protects the nerve cells. 

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