Streptococcus pneumoniae Sialidase SpNanB-Catalyzed One-Pot Multienzyme (OPME) Synthesis of 2,7-Anhydro-Sialic Acids as Selective Sialidase Inhibitors

Abstract

Streptococcus pneumoniae sialidase SpNanB is an intramolecular trans-sialidase (IT-sialidase) and a virulence factor that is essential for streptococcal infection of the upper and lower respiratory tract. SpNanB catalyzes the formation of 2,7-anhydro- N-acetylneuraminic acid (2,7-anhydro-Neu5Ac), a potential prebiotic that can be used as the sole carbon source of a common human gut commensal anaerobic bacterium. We report here the development of an efficient one-pot multienzyme (OPME) system for synthesizing 2,7-anhydro-Neu5Ac and its derivatives. Based on a crystal structure analysis, an N-cyclohexyl derivative of 2,7-anhydro-neuraminic acid was designed, synthesized, and shown to be a selective inhibitor against SpNanB and another Streptococcus pneumoniae sialidase SpNanC. This study demonstrates a new strategy of synthesizing 2,7-anhydro-sialic acids in a gram scale and the potential application of their derivatives as selective sialidase inhibitors.

Fig. 1.

Structures of enzymatically synthesized 2,7-anhydro-Neu5Ac (1) and its chemoenzymatically synthesized derivatives 2–4.

Fig. 2.

Superimposition of 2,7-anhydro-Neu5Ac (in brown sticks), CHES (in pink sticks), and 2-[(3-chlorobenzyl)ammonio)ethanesulfonate (in pale-blue sticks). The coordinates were extracted from Protein Data Bank (PDB IDs: 2WV1, 2VW2, and 4FPF).

Scheme 1.

One-pot multienzyme (OPME) synthesis of 2,7-anhydro-Neu5Ac (1) and 2,7-anhydro-Neu5TFA (2).

Scheme 2.

Synthesis of 2,7-anhydro-Neu5Cyclohexyl (4) from 2,7-anhydro-Neu5TFA (2).