Ingrid 't Hart

97 Chemoenzyma�c synthesis of heptose-ganglioside mimics 5 Isola�on, separa�on and characteriza�on of LOS glycans from C. jejuni has been performed by various techniques. 14,15,16 The presence of C. jejuni molecular mimics in GBS is mainly supported by the detec�on of an�ganglioside an�bodies in pa�ent serum. Various an�ganglioside an�bodies have been iden�fied in serum samples of GBS pa�ents, mainly directed to the gangliosides GM1, GD3, GD1a, GD1b, GT1a, GT1b and GQ1b and rarely to GM2. An�bodies can be directed to one single ganglioside, but also to mixtures of gangliosides. 3,11,17 As an example, an�bodies towards GD1a/GD1b or GQ1b/GM1 complexes have been described and seem to be associated with a severe form of GBS. 18 GM1, GM2 and GM3 are major monosialylgangliosides present in the peripheral nervous system. 19 In addi�on, the gangliosides GM1 and GD1a are highly enriched at the nodes of Ranvier, which is an important loca�on for the genera�on and con�nuance of ac�on poten�als. 20 An�bodies isolated from LOS-immunized rabbits and a GBS pa�ent where shown to cross-react with ganglioside epitopes at the nodes of Ranvier. 21 Furthermore, the GM1 ganglioside is mainly expressed in motor neurons. 22 This explains why GM1 an�bodies are mainly detected in a motor subtype of GBS and in in mul�focal motor neuropathy (MMN), although no C. jejuni infec�ons have been reported preceding MMN. 23 The minimal difference of the LOS ganglioside mimics and the natural gangliosides is the monosaccharide L - glycero - D -manno-heptose (Hep, Figure 1). Heptose is strictly found in microbes and is present in LPS of almost all Gram-nega�ve bacteria. 24 Figure 2. Chemical structures of truncated C. jejuni LOS ganglioside mimics GM3 ( 2 ), GM2 ( 3 ) and GM1 ( 4 ): synthe�c targets for this study. R = (CH) 5 NH 2 linker for immobiliza�on. To study the importance of the heptoside for elici�ng an�bodies cross reac�ve with ganglioside, we aimed to synthesize Hep-gangiloside mimics 2 - 4 (Figure 2). An aminopentyl linker at the reducing end was incorporated for immobiliza�on on NHS- ac�vated microarray slides. Binding of serum an�ganglioside an�bodies of GBS pa�ents to gangliosides and the bacterial heptose-analogs will be compared. Earlier synthe�c efforts have focused on full chemical assembly of LOS oligosaccharides 25 , however bacterial enzymes that can synthesis the ganglio-series oligosaccharides GM3, GM2 and GM1 are readily available. 26 Therefore, we aimed for a chemoenzyma�c approach, star�ng by chemically synthesizing Gal-β1,3-Hep followed by enzyma�c extension to obtain the desired ganglioside mimics. To our knowledge, these truncated LOS structures have not been synthesized before. The heptose-gangliosides will make it possible to gain insight in how GBS serum an�bodies bind to gangliosides and its mimics. OH O O O OH O HO HO HO HO O OR O HO HO HO OH NHAc HOOC O HO OH O AcHN O HO OH HO HO OH O O O OH O HO HO HO HO O OR O HO HO HO OH NHAc HOOC O HO OH HO AcHN OH O O HO OH O HO HO HO HO O OR O HO HO HO OH NHAc HOOC 2 3 4