Diagnostic cyclisation reactions which follow phosphate transfer to carboxylate anion centres for energised [M–H]^– anions of pTyr‐containing peptides

Abstract

The low-energy negative ion phosphoTyr to C-terminal -CO(2)PO(3)H(2) rearrangement occurs for energised peptide [M-H](-) anions even when there are seven amino acid residues between the pTyr and C-terminal amino acid residues. The rearranged C-terminal -CO(2)PO(2)H(O(-)) group effects characteristic S(N)i cyclisation/cleavage reactions. The most pronounced of these involves the electrophilic central backbone carbon of the penultimate amino acid residue. This reaction is aided by the intermediacy of an H-bonded intermediate in which the nucleophilic and electrophilic reaction centres are held in proximity in order for the S(N)i cyclisation/cleavage to proceed. The ΔG(reaction) is +184 kJ mol(-1) with the barrier to the S(N)i transition state being +240 kJ mol(-1) at the HF/6-31 + G(d)//AM1 level of theory. A similar phosphate rearrangement from pTyr to side chain CO(2)(-) (of Asp or Glu) may also occur for energised peptide [M-H](-) anions. The reaction is favourable: ΔG(reaction) is -44 kJ mol(-1) with a maximum barrier of +21 kJ mol(-1) (to the initial transition state) when Asp and Tyr are adjacent. The rearranged species R(1)-Tyr-NHCH(CH(2)CO(2)PO(3)H(-))COR(2) (R(1) = CHO; R(2) = OCH(3)) may undergo an S(N)i six-centred cyclisation/cleavage reaction to form the product anion R(1)-Tyr(NH(-)). This process has a high energy requirement [ΔG(reaction) = +224 kJ mol(-1), with the barrier to the S(N)i transition state being +299 kJ mol(-1)].

Can collision‐induced negative‐ion fragmentations of [M–H]– anions be used to identify phosphorylation sites in peptides?

“…A Tyr phosphate shows the processes [M–H] – → [(M‐H) – – HPO 3 ] and [M–H] – → PO 3 – (Scheme ). The pTyr cleavages are less favourable than the analogous pSer and pThr processes: the loss of HPO 3 and the formation of PO 3 – require +237 and +83 kJ mol –1 at the HF/6‐31+G(d)//AM1 level of theory …”

“…Much of the recent work concerning the identification of phosphorylation sites in peptides and proteins by mass spectrometry has been reviewed . Most studies in this area have involved tandem mass spectrometry using positive‐ion mass spectrometry techniques, but there have also been reports of negative‐ion spectra of phospho‐peptides and proteins . For example, the [M–H] – anions of Ser‐ and Thr‐containing phosphates show the processes [M–H] – → [(M‐H) – – H 3 PO 4 ] and [M–H] – → H 2 PO 4 – (Scheme , R = CHO) [ΔG values at the MP2/6‐31++G(d,p)//HF/6‐31++G(d,p) level of theory] .…”

“…However, there are problems in that phosphate groups can migrate to other centres from pTyr in energised [M–H] – phospho‐peptide ions. The phosphate group of pTyr may be transferred to a C‐terminal CO 2 – (or a C‐terminal CONH − ) group or to a side‐chain CO 2 – group of Asp or Glu . The phosphate rearrangements are low‐energy processes illustrated in Scheme (pTyr to C‐terminal carboxylate rearrangement) and Scheme (pTyr to Asp carboxylate rearrangement) .…”

“…The phosphate rearrangements are low‐energy processes illustrated in Scheme (pTyr to C‐terminal carboxylate rearrangement) and Scheme (pTyr to Asp carboxylate rearrangement) . Each of these rearrangements is followed by S N i (P) cyclisation/cleavage reactions (Schemes and ) all of which have significant energy requirements . In a comprehensive study which includes results from some 18 O‐labelling experiments, Lehmann and coworkers have shown that not only can phosphate rearrangement from pTyr occur to carboxyl groups, but also to side‐chain OH groups .…”

Analysis of creatine phosphate disodium salt by ESI-MS/MS: A seven-centered rearrangement mechanism in gas phase

“…Recently, the application of electrospray ionization mass spectrometry (ESI-MS) has been reported to analyze the phosphoryl molecules [4][5][6][7][8][9][10][11]. Interestingly, several phosphoryl group (P O) participated rearrangement reactions were reported in gas phase, such as phosphoTyr to C-terminal CO 2 PO 3 H 2 rearrangement [7], the phosphoryl rearrangement of P N to P O bonds [8,9], methoxyl group migration [10], and carbonyl oxygen migration [11]. It was found that phosphorus involved rearrangement reactions often go through five-membered intermediate easily, but are difficult to form a six-, especial seven-membered * Corresponding authors.…”