Ingrid 't Hart

57 Synthesis of globo-series glycolipids 3 (VT1, VT2), Gb4 to human and simian parvoviruses and Gb5 and MSGb5 to the human parvovirus. 16,17 More thoroughly studied gangliosides such as GD3 and GT1b are good binders of Siglec-7, an immune receptor mainly found on NK cells. 18,19,20,21 Among the globo-series glycosphingolipids disialylated DSGb5 has also been reported as a Siglec-7 ligand. 22,23 Studying GSLs-protein interac�ons is challenging, since the isola�on of GSLs usually provides heterogeneous mixtures and poten�al impuri�es. Besides, most trans interac�ons are thought to take place through the GSL glycan moie�es. Therefore, most studies focus on the synthesis of the GSL glycan moie�es. 24,25 We and others have synthesized globo-series oligosaccharides, by chemical synthesis 26,27 , chemoenzyma�c synthesis 28,29,30, or enzyma�c synthesis. 24,31 Recent studies have a�ributed important binding interac�ons to the ceramide moiety of GSLs. One study demonstrated that milk-derived GD3 did bind Siglec-7, whereas GD3 expressed by DLD-1 cells did not bind this receptor. Structural differences were found in the ceramide moie�es and turned out to be the reason for altera�ons in protein binding. These ceramide modifica�ons were only small: phytosphingosine instead of sphingosine or an α-hydroxyl on the fa�y acid. 32 Another study focused on how changes in lipid composi�on of Gb3 affects VT binding. In this study, shorter fa�y acid chains (C12, C14) showed li�le binding, whereas intermediate and long fa�y acid chains (C16-C24) showed stronger binding to VT. Also, unsaturated fa�y acid moie�es significantly increased VT binding. 33 These studies, suggest that ceramides can directly interact with proteins such as VT. The ceramide composi�ons can also affect ra� forma�on with other components such as cholesterol, resul�ng in different presenta�ons, which in turn may influence protein binding. 17 Basedon the abovedescribedobserva�ons, we envisaged that thepresenceof a ceramide ofglobo-seriesGSLswillaffectproteinbinding. Toillustratethedifferencesofthepreviously used 28 short (C5) aminopentyl linker (Fig. 2A), and the more complex ceramide moiety, structural analogues of Gb5 are presented in Fig. 2B. Chemically well-defined compounds are needed to be synthesized to inves�gate the importance of the ceramide moiety. Figure 2. ( A ) Globo-series glycan moie�es with an aminopentyl linker for microarray (Chapter 2). ( B ) Natural globo-series glycosphingolipids with natural ceramide, where the fa�y acid chain length can vary between 14 to >30. R 1 = R 2 = H: Gb5 | R 1 = α2,3Neu5Ac, R 2 = H: MSGb5 | R 1 = α2,3Neu5Ac, R 2 = α2,6Neu5Ac: DSGb5. O HO OR 2 O AcHN O HO OH O HO O O OH HO OH O O OH HO OH HN OH (CH 2 ) 12 CH 3 O (CH 2 )nCH 3 O O HO OH R 1 O HO O HO OR 2 O AcHN O HO OH O HO O O OH HO OH O O OH HO OH O O HO OH R 1 O HO NH 2 A B