Phosphoamino acids

Alkaline hydrolysis (with NaOH, KOH or more seldom with Ba(OH)2) is almost exclusively applied for the determination of tryptophan and phosphoamino acids. Serine, threonine, arginine, and cysteine are completely destroyed by alkaline hydrolysis, while other amino acids are racemized [190]. Since racemization also occurs during acid hydrolysis, when it is important to... 

The hydrolysis conditions of phosphoamino acids with respect of stability and reproducibility of quantitative determination are discussed by Bylund and Huang (1976). Anal Biochem 73 477). 

A. Otaka, E. Mitsuyama, J. Watanabe, H. Watanabe, N. Fujii, Synthesis of fluorine-containing bioisosteres corresponding to phosphoamino acids and dipeptide units. Biopolymers 76 (2004) 140-149. 

Since the first chemical studies into the preparation of simple phosphoserine-peptides in 1959, several synthetic approaches have been investigated for the solution or solid-phase synthesis of phosphorylated peptides containing phosphoserine Ser(P), phosphothreonine Thr(P), and phosphotyrosine Tyr(P) residues. This section outlines two main methods for the synthesis of phosphorylated peptides which involve (1) the specific incorporation of protected phosphoamino acids in Boc or Fmoc peptide synthesis or (2) the post-assembly phosphorylation of Ser-, Thr- or Tyr-containing peptide-resins. For comprehensive recent reviews on the synthesis of phosphorylated peptides, the reader is directed to refs[141142l... 

Alkaline hydrolysis with barium, sodium, or lithium hydroxides (0.2-4 M) at 110°C for 18-70 h126-291 requires special reaction vessels and handling. Reaction mixtures are neutralized after hydrolysis and barium ions have to be removed by precipitation as their carbonate or sulfate salts prior to analysis which leads to loss of hydrolysate. Correspondingly, peptide contents are difficult to perform by this procedure. Preferred conditions for alkaline hydrolysis are 4M LiOH at 145 °C for 4-8 h where >95% of tryptophan is recovered 291 An additional inconvenience of the alkaline hydrolysis procedure is the dilution effect in the neutralization step and thus the difficult application to the analyzer if micro-scale analysis is to be performed. The main advantage is the good recovery of tryptophan and of acid-labile amino acid derivatives such as tyrosine-0-sulfate1261 (Section 6.6) as well as partial recovery of phosphoamino acids, particularly of threonine- and tyrosine-O-phosphate (Section 6.5). 

It has been shown that phosphorylation changes the local conformation of a protein and thereby affects the activity of the complete protein. 341 Phosphorylation of serine and threonine side chains often occurs (Scheme 2). Phosphoamino acids are readily characterized using 3H and 31P NMR experiments. The H and 31P NMR parameters are distinct for phosphorylated serine, threonine, and tyrosine and have also been used to identify both cis-and trans-O-phospho-4-hydroxy-L-proline. 35 Phosphorylation of Cys is rare, but it can be identified by NMR even in large proteins. 36 ... 

Direct Incorporation of Fmoc Phosphoamino Acid Derivatives... 

Partially protected phosphoamino acids (Novabiochem, see Note 4) ... 

To our experience, it is difficult to couple more than one phosphoamino acid derivative in one peptide. This is due to a reduced reactivity and/or sterical hindrance, especially if two phosphoamino acids are in close proximity. 

Kamps, M.P., Sefton, B.M (1989) Acid and Base Hydrolysis of Phosphoproteins Bound to Immo-bilon Facilitates the Analysis of Phosphoamino Acids in Gel-Fractionated Proteins, Anal. Biochem. 176, 22-27. 

Initially we used an extraction solvent (S3) of 90% methanol (7) and obtained phosphoamino acid sequence data which was confirmed by other methods (9). However we changed the extraction solvent to trifluoroacetic acid as used by Meyer et al., (2) and Russo et al. (8) because of its greater efficiency. 

In Fig. 6 we show a phosphopeptide whose amino acid sequence was determined in a normal run and whose phosphoamino acid sequence was determined by the methods described above. According to the published sequence, cysteine is present at position 4, but because it was not all lated, it was not seen in this run. The absence of an amino acid at position 7 is consistent with phosphoserine, as expected from the published amino acid sequence (10). 

The O-trityl protection can be removed under the same conditions as used for cleavage of peptides from 2-chlorotrityl resin, i.e. with ACOH/TFE/CH2Q2 (2 2 6, rt, 1 h) as the cleavage nnixture or with 1% TFA without affecting tert-butyl side-chain protection. Silanes are added as hydride donors to scavenge the trityl cations and to avoid retritylation. Most commonly, the trityl derivatives of tyrosine, serine, and threonine are used for the synthesis of phosphopeptides by postsynthetic methods on a solid support. In contrast to the use of protected phosphoamino acid derivatives, such as Fmoc-Tyr(POOBzl)-OH,f l both the phosphorylated and nonphosphorylated peptides can be prepared from one syn-... 

The chemistry of three phosphoamino acids isolated from biological material. 

One of the characteristic features of these three phosphoamino acids is that in contrast to the intact proteins, the phosphate group is stable in 0.25 N sodium hydroxide (72). The N-—P bond of phosphoarginine, however, is acid-labile. 

Following this discussion of some of the properties of three naturally occurring phosphoamino acids and of the dipeptide, 0-phosphorylseryl-glutamic acid, a few examples of phosphoproteins, i.e., casein, vitellin, vitellenin, and phosvitin, and of the phosphopeptones derived from these materials, will be considered. 

From these observations it follows that (1) some of the chemical properties of a phosphoamino acid may change considerably on incorporation into a peptide or protein, (2) that the adjacent molecular configuration may be responsible for the stability of the phosphate group, and (3) that the acidity of the medium determines whether migration of a phosphoric acid residue from the —0— to the —— position occurs. As outlined in a previous section in this article A-phosphorylserine and A-phosphorylthreonine, respectively, w-ould represent possible configurations of the A-terminal amino acid of a peptide chain in a native protein. 

A second property in common to all phosphoproteins is the great lability of the phosphate groups in dilute alkali, in contrast to the stability of phosphoamino acids in this medium. 

Park. S.B., and Standaert. R.R. a,a-Difluorophosphonomethyl azobenzene derivatives as photo-regulated phosphoamino acid analogs. Part 1. Design and synthesis. Tetrahedron Lett.. 40. 6557, 1999. 

A-Phosphoryl sulfamates (66) can be considered bioisosteres of pyrophosphate. Compounds (66) have now been prepared by the reaction of sulfamates (64) with trialkyl phosphites to give (65) which readily isomerise under basic conditions. A variety of N-phosphoamino acids (67) carrying long-chain alkyl groups on phosphorus have been prepared from the corresponding dialkyl phosphite and amino acids (Scheme 8). A modified approach to the solid-phase... 

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