Serine, conjugation

Deacetylation and catalytic hydrogenation with Pearlman s catalyst, in the absence of any asymmetric catalyst, afforded the serine conjugate 109 in a 6 1 ratio in favor of the desired (L)-isomer. 

Taurine conjugation with bile acids, phenylacetic acid, and indolylacetic acid seems to be a minor process in most species, but in the pigeon and ferret, it occurs extensively. Other infrequently reported conjugations include serine conjugation of xanthurenic acid in rats excretion of quinaldic acid as quinaldylglycyltaurine and quinaldylglycylglycine in the urine of the cat, but not of the rat or rabbit and conversion of furfural to furylacrylie acid in the dog and rabbit, but not in the rat, hen, or human. The dog and... 

Figure 1.107 The N-terminal aldehyde group on a peptide formed from periodate oxidation of serine or threonine residues can be conjugated with a hydrazide-containing molecule to produce a hydrazone bond.

Geoghegan, K.E, and Stroh, J.G. (1992) Site-directed conjugation of nonpeptide groups to peptides and proteins via periodate oxidation of a 2-amino alcohol. Applications to modification at N-terminal serine. Bioconjugate Chem. 3, 138-146. 

The amounts of single amino acids excreted in urine in the conjugated form, as determined independently by Stein and Muting, are given in Tables 1 and 2. According to Stein, glycine, glutamic acid, aspartic acid, histidine, and proline are quantitatively the most important amino acids liberated in the course of urine hydrolysis. Serine, lysine, tyrosine, cysteine and cystine, threonine, alanine, valine, phenylalanine, and leucine are... 

Fig. 6.25. Simplified mechanism of two degradation reactions between peptides and reducing sugars occurring in solids, a) Maillard reaction between a side-chain amino (or amido) group showing the formation of an imine (Reaction a), followed by tautomerization to an enol (Reaction b) and ultimately to a ketone (Reaction c). Reaction c is known as the Amadori rearrangement (modified from [8]). b) Postulated mechanism of the reaction between a reducing sugar and a C-terminal serine. The postulated nucleophilic addition yields an hemiacetal (Reaction a) and is followed by cyclization (intramolecular condensation Reaction b). Two subsequent hydrolytic steps (Reactions c and d) yield a serine-sugar conjugate and the des-Ser-peptide...

Suitably protected amino acids (112) (cysteine, serine, and lysine) have been added via the side-chain heteroatom (S, O, and N, respectively) to conjugated alkynones, alkynoic ester and alkynoic amide (113). The expected heterosubstituted vinyl product (114) was formed in each case, mainly as the ii-isomer. In an accompanying paper, this type of addition was applied to the derivatives of fluorescein, 7-hydroxycoumarin, Sudan 1, and dansyl chloride with linker arms containing a conjugated terminal alkyne. 

Thus, a new and convenient procedure has been developed by Defrancq and coworkers for the synthesis of 3 -ohgonucleotide conjugates 83 through the formation of glyoxyhc oxime bonds (Scheme 44). This has been achieved by using a novel sohd support 82 for ODN synthesis. Support 82 was conveniently prepared from a commercially available serine derivative in a few steps. The glyoxylic oxime bonds showed higher stability than aldoxime bonds at acidic to neutral pH but lower stabihty at alkaline pH. 

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