Galactosyl and sialyl clusters: synthesis and evaluation against T. cruzi parasite

Abstract

The multivalent effect of carbohydrates (glycoclusters) has been explored to study important biological targets and processes involving Trypanosoma cruzi (T. cruzi) infection. Likewise, CuAAC cycloaddition reactions (click chemistry) have been applied as useful strategy in the discovery of bioactive molecules. Hence, we describe the synthesis of 1,2,3-triazole-based tetravalent homoglycoclusters (1–3) and heteroglycoclusters (4 and 5) of d-galactopyranose (C-1 and C-6 positions) and sialic acid (C-2 position) to assess their potential to inhibit T. cruzi cell invasion and also its cell surface trans-sialidase (TcTS). The target compounds were synthesised in good yields (52–75 %) via click chemistry by coupling azidosugars galactopyranose and sialic acid with alkynylated pentaerythritol or tris(hydroxymethyl)-aminomethane (TRIS) scaffolds. T. cruzi cell invasion inhibition assays showed expressive low parasite infection index values (5.3–6.8) for most compounds. However, most glycoclusters proved to be weak TcTS inhibitors at 1 mM (<17 %), except the tetravalent sialic acid 3 (99 % at 1 mM, IC50 450 μM). Therefore, we assume that T. cruzi cell invasion blockage is not due to TcTS inhibition by itself, but rather by other mechanisms involved in this process. In addition, all glycoclusters were not cytotoxic and had significant trypanocidal activity upon parasite survival of amastigote forms.

Anomeric 1,2,3-triazole-linked sialic acid derivatives show selective inhibition towards a bacterial neuraminidase over a trypanosome trans-sialidase

“…A small series of anomeric 1,2,3-triazole-linked sialic acid derivatives was synthesised as outlined in Figure 2B . Emulating our previous work with anomeric azide CuAAC click chemistry [ 17 , 22 – 24 ], the well-known α-azidosialic acid 1 [ 25 ] was synthesised from N -acetylneuraminic acid in four steps [ 26 ] in good overall yield (55%). The assignment of the anomeric configuration of 1 was based on the chemical shift of H 3eq , which is located in lower magnetic field (over 2.5 ppm) when compared to a β-glycoside (under 2.5 ppm) [ 27 ].…”

“…Although TcTS is the major parasite virulence factor [ 13 ], there is no nanomolar inhibitor developed to date. The most potent TcTS inhibitors described are non-carbohydrate-based molecules (anthraquinones [ 14 ], chalcones and quinolones [ 15 ]) with low micromolar activity, whereas sialic acid-based analogues typically show high millimolar inhibitory activity [ 16 ], with few exceptions such as a pentaerythritol homoglycocluster reported by the Carvalho group [ 17 ] and a C -sialoside bearing phenylpropyl group at C-2 [ 18 ] ( Figure 1C ). In the context of mimicking the terminal sugars α-ᴅ-Neu5Ac(2,3)-β-ᴅ-Gal of Trypanosoma cruzi mucins to obtain potent TcTS inhibitors, our group previously synthesised a small series of C-2-modified sialic acid bearing a monosaccharide tethered via 1,2,3-triazole ring (sialylmimetic neoglycoconjugates) [ 19 ] that showed 67–91% inhibitory activity at 1 mM.…”

Anomeric 1,2,3-triazole-linked sialic acid derivatives show selective inhibition towards a bacterial neuraminidase over a trypanosome trans-sialidase

“…A small series of anomeric 1,2,3-triazole-linked sialic acid derivatives was synthesised as outlined in Figure 2B. Emulating our previous work with anomeric azide CuAAC click chemistry [17,[20][21][22], the well-known α-azido sialic acid 1 [23] was synthesised from N-acetylneuraminic acid in four steps [24] in good overall yield (55%), and used as a key intermediate for further CuAAC reaction [25][26][27][28] with eleven (hetero)aromatic and non-aromatic terminal alkynes readily available in our lab [21]. Although CuAAC is reputedly tolerant of a broad range of substrates, solvents, and reaction conditions; all these parameters have to be carefully planned to avoid low yields or even no product formation, as previously described for compound 1 [29].…”

“…Although TcTS is the major parasite virulence factor [13], there is no nanomolar inhibitor developed to date. The most potent TcTS inhibitors described are non-carbohydrate-based molecules (anthraquinones [14], chalcones and quinolones [15]) with low micromolar activity, whereas sialic acid-based analogues typically show high millimolar inhibitory activity [16], with few exceptions such as a pentaerythritol homoglycocluster reported by the Carvalho group [17] and a C-sialoside bearing phenylpropyl group at C-2 [18] (Figure 1C). Based on our previous approach with a small series of C-2 modified sialic acid bearing a monosaccharide tethered via 1,2,3-triazole ring (sialylmimetic 3 neoglycoconjugates) [19], which showed 67-91% inhibitory activity at 1mM, we now envisaged replacing the monosaccharide moiety by (hetero)aromatic substituents (Figure 2A) expecting better inhibition with hydrophobic substituents as observed for the high affinity reported for C-sialoside.…”

Sialidase and Sialyltransferase Inhibitors: Targeting Pathogenicity and Disease

“…To this end, a group of unusual triazole linked sialic acid and galactose disaccharides were devised in one study, resulting in a lead compound with µM potency against T. cruzi trans-SA (16) ( Campo et al, 2012 ). More recently, multivalent sugar syntheses were attempted to find new trypanosome trans-SA inhibitors, with the most successful compound (17, a tetra-sialic acid conjugate) exhibiting 99% inhibition at 1 mM and an IC 50 of 450 µM ( Figueredo et al, 2019 ). Unfortunately, the inclusion of multiple sugars is likely to give poor absorbance and low bioavailability, highlighting the need for further research.…”