jp9b04143_si_001.pdf (193.8 kB)
Toward Closing the Gap between Hexoses and N‑Acetlyhexosamines: Experimental and Computational Studies on the Collision-Induced Dissociation of Hexosamines
journal contribution
posted on 2019-07-26, 18:38 authored by Cheng-chau Chiu, Hai Thi Huynh, Shang-Ting Tsai, Hou-Yu Lin, Po-Jen Hsu, Huu Trong Phan, Arya Karumanthra, Hayden Thompson, Yu-Chi Lee, Jer-Lai Kuo, Chi-Kung NiMotivated by the
fundamental difference in the reactivity of hexoses
and N-acetylhexosamines under collision-induced dissociation
(CID) mass spectrometry conditions, we have investigated the CID of
two hexosamines, glucosamine (GlcN) and galactosamine (GalN), experimentally
and computationally. Both hexosamines undergo ring-opening and then
dissociate via the 0,2A and the 0,3A (0,3X) cross-ring cleavage channels. The preference for the ring-opening
is similar to the behavior of N-acetylhexosamines
and explains why the two anomers of the same sugar give the same mass
spectrum. While the spectrum for GlcN is dominated by the 0,2A signal, the signal intensities for both 0,2A and the 0,3A (0,3X) dissociation channels are comparable
for GalN, which allows GlcN and GalN to be distinguished easily. Calculations
at MP2 level of theory indicate that this is related to the differences
in the relative barrier heights for the 0,2A and the 0,3A (0,3X) cross-ring cleavage channels. This,
in return, reflects the circumstance that the 0,2A cross-ring
cleavage barriers are different for the two sugars, while the barriers
of all other dissociation channels are comparable. While the mechanisms
of the cross-ring dissociation channels of hexoses are well described
using the retro–aldol mechanism in the literature, this study
proposes a new mechanism for the 0,3A (0,3X)
cross-ring cleavage of hexosamines that involves the formation of
an epoxy intermediate or a zwitterionic intermediate.