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Mass spectral study of Boc-carbo-beta3-peptides: differentiation of two pairs of positional and diastereomeric isomers.
J Mass Spectrom. 2004 Sep; 39(9):1068-74.JM

Abstract

A mass spectral study of a series of new Boc-C-linked carbo-beta(3)-peptides prepared from C-linked carbo-beta(3)-amino acids (Caa) was carried out using liquid secondary ion mass spectrometry (LSIMS), electrospray ionization (ESI) and tandem mass spectrometry. Using the nomenclature of Roepstorff and Fohlman, the positive ion high- and low energy collision-induced dissociation (CID) of [M + H - Boc + H](+) ions of the peptides produce both N- and C-terminus ions, y(n) (+) and b(n) (+) ions, with high abundance and other ions of low abundance. Further, characteristic fragment ions of carbohydrate moiety are observed. In contrast to the CID of protonated peptide acids, the CID of [M - H](-) ions of the beta(3)-peptide acids do not give b(n)(-) ions and show abundant z(n)(-) and c(n) (-) ions which are insignificant in the former. Two pairs of positionally isomeric Boc-carbo-beta(3)-dipeptides were differentiated by the CID of [M + H](+) ions in LSIMS and ESIMS. The fragment ion [M + H - C(CH(3))(3) + H](+) formed from [M + H](+) by the loss of 2-methylprop-2-ene is relatively more abundant in the dipeptide Boc-NH-beta-hGly-Caa(S)-OCH(3) (14) containing the sugar moiety at the C-terminus whereas it is insignificant in Boc-NH-Caa(S)-beta-hGly-OCH(3) (13), which has the sugar moiety at the N-terminus. Similarly, two pairs of diastereomeric dipeptides were distinguished by the high- and low-energy CID of [M + H](+) ions. The loss of 2-methylprop-2-ene is more pronounced for Boc-NH-Caa(R)-beta-hGly-OCH(3) (17) and Boc-NH-Caa(R)-Caa(S)-OCH(3) (18) isomers whereas it is insignificant for Boc-NH-Caa(S)-beta-hGly-OCH(3) (13) and Boc-NH-Caa(S)-Caa(S)-OCH(3) (2) isomers. This was attributed to a favorable configuration of the carbohydrate moiety favoring the 'H' migration involved in the loss of 2-methylprop-2-ene from the [M + H](+) ions of isomers 17 and 18 compared with the unfavorable configuration of the carbohydrate moiety in isomers 13 and 2.

Authors+Show Affiliations

National Center for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad 500007, India.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

15386745

Citation

Srikanth, R, et al. "Mass Spectral Study of Boc-carbo-beta3-peptides: Differentiation of Two Pairs of Positional and Diastereomeric Isomers." Journal of Mass Spectrometry : JMS, vol. 39, no. 9, 2004, pp. 1068-74.
Srikanth R, Nagi Reddy P, Narsimha R, et al. Mass spectral study of Boc-carbo-beta3-peptides: differentiation of two pairs of positional and diastereomeric isomers. J Mass Spectrom. 2004;39(9):1068-74.
Srikanth, R., Nagi Reddy, P., Narsimha, R., Srinivas, R., Sharma, G. V., Ravinder Reddy, K., & Radha Krishna, P. (2004). Mass spectral study of Boc-carbo-beta3-peptides: differentiation of two pairs of positional and diastereomeric isomers. Journal of Mass Spectrometry : JMS, 39(9), 1068-74.
Srikanth R, et al. Mass Spectral Study of Boc-carbo-beta3-peptides: Differentiation of Two Pairs of Positional and Diastereomeric Isomers. J Mass Spectrom. 2004;39(9):1068-74. PubMed PMID: 15386745.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Mass spectral study of Boc-carbo-beta3-peptides: differentiation of two pairs of positional and diastereomeric isomers. AU - Srikanth,R, AU - Nagi Reddy,P, AU - Narsimha,R, AU - Srinivas,R, AU - Sharma,G V M, AU - Ravinder Reddy,K, AU - Radha Krishna,P, PY - 2004/9/24/pubmed PY - 2005/2/11/medline PY - 2004/9/24/entrez SP - 1068 EP - 74 JF - Journal of mass spectrometry : JMS JO - J Mass Spectrom VL - 39 IS - 9 N2 - A mass spectral study of a series of new Boc-C-linked carbo-beta(3)-peptides prepared from C-linked carbo-beta(3)-amino acids (Caa) was carried out using liquid secondary ion mass spectrometry (LSIMS), electrospray ionization (ESI) and tandem mass spectrometry. Using the nomenclature of Roepstorff and Fohlman, the positive ion high- and low energy collision-induced dissociation (CID) of [M + H - Boc + H](+) ions of the peptides produce both N- and C-terminus ions, y(n) (+) and b(n) (+) ions, with high abundance and other ions of low abundance. Further, characteristic fragment ions of carbohydrate moiety are observed. In contrast to the CID of protonated peptide acids, the CID of [M - H](-) ions of the beta(3)-peptide acids do not give b(n)(-) ions and show abundant z(n)(-) and c(n) (-) ions which are insignificant in the former. Two pairs of positionally isomeric Boc-carbo-beta(3)-dipeptides were differentiated by the CID of [M + H](+) ions in LSIMS and ESIMS. The fragment ion [M + H - C(CH(3))(3) + H](+) formed from [M + H](+) by the loss of 2-methylprop-2-ene is relatively more abundant in the dipeptide Boc-NH-beta-hGly-Caa(S)-OCH(3) (14) containing the sugar moiety at the C-terminus whereas it is insignificant in Boc-NH-Caa(S)-beta-hGly-OCH(3) (13), which has the sugar moiety at the N-terminus. Similarly, two pairs of diastereomeric dipeptides were distinguished by the high- and low-energy CID of [M + H](+) ions. The loss of 2-methylprop-2-ene is more pronounced for Boc-NH-Caa(R)-beta-hGly-OCH(3) (17) and Boc-NH-Caa(R)-Caa(S)-OCH(3) (18) isomers whereas it is insignificant for Boc-NH-Caa(S)-beta-hGly-OCH(3) (13) and Boc-NH-Caa(S)-Caa(S)-OCH(3) (2) isomers. This was attributed to a favorable configuration of the carbohydrate moiety favoring the 'H' migration involved in the loss of 2-methylprop-2-ene from the [M + H](+) ions of isomers 17 and 18 compared with the unfavorable configuration of the carbohydrate moiety in isomers 13 and 2. SN - 1076-5174 UR - https://www.unboundmedicine.com/medline/citation/15386745/Mass_spectral_study_of_Boc_carbo_beta3_peptides:_differentiation_of_two_pairs_of_positional_and_diastereomeric_isomers_ L2 - https://doi.org/10.1002/jms.690 DB - PRIME DP - Unbound Medicine ER -