A photoreactive competitive inhibitor of the human lysosomal neuraminidase in cultured skin fibroblasts

Polyvalent Transition-State Analogues of Sialyl Substrates Strongly Inhibit Bacterial Sialidases*

Bacterial sialidases (SA) are validated drug targets expressed by common human pathogens such as Streptococcus pneumoniae, Vibrio cholerae, or Clostridium perfringens. Noncovalent inhibitors of bacterial SA capable of reaching the submicromolar level are rarely reported. In this work, multi- and polyvalent compounds are developed, based on the transition-state analogue 2-deoxy-2,3-didehydro-N-acetylneuraminic (DANA). Poly-DANA inhibits the catalytic activity of SA from S. pneumoniae (NanA) and the symbiotic microorganism B. thetaiotaomicron (BtSA) at the picomolar and low nanomolar levels (expressed in moles of molecules and of DANA, respectively). Each DANA grafted to the polymer surpasses the inhibitory potential of the monovalent analogue by more than four orders of magnitude, which represents the highest multivalent effect reported so far for an enzyme inhibition. The synergistic interaction is shown to operate exclusively in the catalytic domain, and not in the flanked carbohydrate-binding module (CBM). These results offer interesting perspectives for the multivalent inhibition of other SA families lacking a CBM, such as viral, parasitic, or human SA.

Synthesis of C-5 Analogs of N-Acetylneuraminic Acid via Indium-Mediated Allylation of N-Substituted 2-Amino-2-deoxymannoses

This paper presents a short synthesis of new analogs of N-acetylneuraminic acid (Neu5Ac) varied structurally at C-5. The synthetic strategy includes indium-mediated coupling reactions between ethyl 2-(bromomethyl)acrylate and N-derivatized mannosamines, and the ozonolysis of the resulting enoates. The main advantage of this indium-mediated allylation for the synthesis of neuraminic acids comes from the efficient, stereoselective C-C bond formation, which affords predominantly the correct diastereomer having a threo relationship between the newly generated hydroxyl group and the C-2 amide group of mannosamine. By this approach, Neu5Boc (4a), Neu5Gly (4b), Neu5(6-NHCbz)hexanoyl (4c), and Neu5(1-naphthyl)acetyl (4d) were prepared in three steps (overall approximately 50%). In addition, several N-substituted neuraminic acids were synthesized by N-acylation of the amino functionality of neuraminic acid (5b), which was obtained by deprotecting the N-Boc group of Neu5Boc (4a). These analogs include Neu5BrAc (6a), Neu5acryloyl (6b), Neu5benzoyl (6c) and Neu5benzoyl-4-benzoyl (6d). The N-acylation method is especially suited for synthesis of neuraminic acids bearing substituents that can not tolerate ozonolysis or that are unstable (photo)chemically. Finally, we illustrate the utility of synthetic neuraminic acids by converting 4c to a derivative of 2-deoxy-2,3-didehydroneuraminic acid (8c), a precursor to inhibitors of neuraminidases.

Photolabelling of Salmonella typhimurium LT2 sialidase. Identification of a peptide with a predicted structural similarity to the active sites of influenza-virus sialidases

The sialidase from Salmonella typhimurium LT2 was characterized by using photoaffinity-labelling techniques. The well-known sialidase inhibitor 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non- 2-enonic acid (Neu5Ac2en) was modified to contain an amino group at C-9, which permitted the incorporation of 4-azidosalicylic acid in amide linkage at this position. Labelling of the purified protein with the radioactive (125I) photoprobe was determined to be highly specific for a region within the active-site cavity. This conclusion was based on the observation that the competitive inhibitor Neu5Ac2en in the photolysis mixture prevented labelling of the protein. In contrast, compounds with structural and chemical features similar to the probe and Neu5Ac2en, but which were not competitive enzyme inhibitors, did not affect the photolabelling of the protein. The peptide interacting with the probe was identified by CNBr treatment of the labelled protein, followed by N-terminal sequence analysis. Inspection of the primary structure of the protein, predicted from the cloned structural gene for the sialidase [Hoyer, Hamilton, Steenbergen & Vimr (1992) Mol. Microbiol. 6, 873-884] revealed that the label was incorporated into a 9.6 kDa fragment situated within the terminal third of the molecule near the C-terminal end. Secondary-structural predictions using the Garnier-Robson algorithm [Garnier, Osguthorpe & Robson (1978) J. Mol. Biol. 120, 97-120] of the labelled peptide revealed a structural similarity to the active site of influenza-A- and Sendai-HN-virus sialidases with a repetitive series of alternating beta-sheets connected with loops.

Distinguishing mammalian sialidases by inhibition kinetics with novel derivatives of 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic acid, an unsaturated derivative of N-acetylneuraminic acid

Kinetic analysis of mammalian sialidases was carried out using analogs of the potent sialidase inhibitor, 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic+ ++ acid (1). Substitutents at C-9 in place of the terminal hydroxyl group included a, 4-azido-2-nitrophenylthio group to give 5-acetamido-2,6-anhydro-9-S-(4-azido-2-nitrophenyl)-3,5, 9-trideoxy-9-thio-D-glycero-D-galacto-non-2-enonic acid (2), and an azide group to give 5-acetamido-2,6-anhydro-9-azido-3,5,9-trideoxy-D-glycero-D-galacto-non-2 -enonic acid (3). Competitive inhibition kinetics were observed when 1,2, and 3 were tested with the lysosomal sialidase (cultured fibroblasts) and the plasma membrane sialidase (adenovirus DNA-transformed, human embryonic kidney cells), giving a Ki of about 10 microM for both enzymes with all three compounds. In contrast, only 1 was a potent inhibitor of the microsomal sialidase (rat muscle).

Photolabeling of the alpha-neuraminidase/beta-galactosidase complex from human placenta with a photoreactive neuraminidase inhibitor

Photolabeling of the alpha-neuraminidase/beta-galactosidase complex in human placenta (Verheijen, F.W. et al (1987) Eur. J. Biochem. 162, 63-67) was carried out using the radioactive photoprobe, 9-S-(4-azido-3,5-3H-2-nitrophenyl)-5-acetamido-2,6 anhydro-2,3,5,9- tetradeoxy-9- thio-D-glycero-D-galacto-non-2-enonic acid. Two intensely labeled bands at 61 and 46 kD were detected with autoradiography. Labeling of the 46 kD protein was blocked with the inclusion of the surfactant Triton X-100 in the photolysis mixture, indicating a nonspecific, hydrophobic interaction. The 61 kD protein was protected from labeling only when the neuraminidase inhibitor 2,3 dehydro N-acetyl neuraminic acid (1 mM) was present during photolysis. These results suggest that the neuraminidase activity resides among the proteins in the 61 kD molecular weight range comigrating with the lysosomal beta-galactosidase, under denaturing conditions.