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. Author manuscript; available in PMC: 2020 Nov 27.
Published in final edited form as: J Am Chem Soc. 2019 Nov 18;141(47):18851–18861. doi: 10.1021/jacs.9b10376

Figure 2.

Figure 2.

The caC base is a monoanion at physiological pH and N-glycosyl bond hydrolysis is likely precluded by the poor leaving-group (LG) quality of a departing caC dianion. For clarity, the focus is on LG departure in a stepwise mechanism (oxacarbenium ion intermediate), without showing details for nucleophile addition (see text). Leaving group quality is improved by protonation of the caC anion to give a neutral species (amine, zwitterion, or imino), as shown by previously calculated N1 acidities, where the free energy of deprotonation (kcal mol−1) in water is 27.7 for the caC anion and 20.5, 13.3, and 16.0 for the amino, zwitterion, and imino forms of neutral caC, respectively.21