Development of the synthetic method for the preparation of dimannosylated desmuramylpeptides

Abstract

Lektini su komplementarni proteini koji specifično prepoznaju ugljikohidrate. Dijele se na pet osnovnih skupina s obzirom na šećer prema kojem pokazuju najveći afinitet. Jedna od skupina lektina su manozni receptori (MR) koji specifično prepoznaju manozu. Nalaze se na površini endotelnih stanica te na makrofagima, a imaju ulogu u urođenoj imunosti. Dokazano je da ligandi s dvije ili više manoznih podjedinica, pokazuju povećani afinitet prema lektinima. Vezanjem manoze na imunostimulatorne (adjuvantske) supstance moguće je pojačati njihovu aktivnost. Muramildipeptid (MDP, N-acetilmuramil-L-Ala-D-isoGln) najmanja je strukturna jedinica peptidoglikana koja pokazuje imunostimulatornu (adjuvantsku) aktivnost. Obzirom da se MDP slabo unosi u makrofage i brzo eliminira, te pokazuje pirogeno i artritogeno djelovanje, dizajniraju se novi imunomodulatori s poboljšanim farmakološkim svojstvima. U sklopu ovog rada razvijena je sintetska metoda za pripravu dimanoziliranih derivata desmuramilpeptida s potencijalnom adjuvantskom aktivnošću. Učinkovitost metode dokazana je na pripravi (2S)-2,6-di[2-(α-D-manopiranoziloksi)acetilamino]heksanoil-L-alanil-D-izoglutamina (10). Prvo je sintetizirana 2-(2,3,4,6-tetra-O-acetil-α-D-manopiranoziloksi)octena kiselina supstitucijom broma iz t-butil-bromacetata s tetraacetiliranom manozom α-konfiguracije. Dobivenom manozidu je uklonjena esterska zaštita s karboksilne skupine preko koje je potom karbodiimidnom metodom uz EDC/HOBt aktivaciju vezan benzilni ester L-lizina. Nakon uklanjanja benzilne zaštite s lizina dobivena je (2S)-2,6-di[2-(2,3,4,6-tetra-O-acetil-α-D-manopiranoziloksi)acetilamino]heksanska kiselina koja je konjugirana s desmuramildipeptidom, benzilnim esterom L-alanil-D-izoglutamina. U posljednjoj fazi uklonjene su zaštitne skupine, acetatne zaštite s manoznih podjedinica te benzilna zaštite s D-izoglutamina. Svi sintetizirani spojevi su strukturno okarakterizirani NMR spektroskopijama, spektrometrijom masa, a neki od njih i IR spektroskopijom.Lectins are complementary proteins that specifically recognise carbohydrates. They can be divided into five major groups, depending on the sugar towards they have biggest affinity. One of those are mannose receptors (MR) which specifically recognise mannose. They are located on the surface of endothelial cells and on macrophagesand they participate in innate immunity. It is proven that ligands with two or more mannose subunits exhibit increased affinity towards lectins. Binding of mannose on an immunostimulant can increase their adjuvant activity. Muramyl dipeptide (MDP, N-acetylmuramil-L-Ala-D-isoGln) is the smallest peptidoglycan structural unit that show adjuvant activity. Since MDP is characterized with low uptake into macrophages, fast elimination also pyrogenic and arthritogenic activity, new immunomodulators with improved pharmacological properties are being designed. In the scope of this Diploma Thesis, novel method for synthesis of dimannosylated desmuramylpeptide with potential adjuvant activity was developed. Effectiveness of the method was proven on the synthesis of (2S)-2,6-di[2-(α-D-mannopyranosyloxi)acetylamino]hexanoyl-L-alanyl-D-isoglutamine (10). At first, 2-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyloxi)acetic acid was synthesized by the substitution of bromine from t-butyl-bromoacetate with α-anomer of tetraacetylated mannose. After the ester protection was removed, benzyl ester of L-lysine was connected to the mannoside using the EDC/HOBt carbodiimide method. Removal of benzyl protection from the lysine resulted with (2S)-2,6-di[2-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyloxi)acetylamino]hexanoic acid which was then conjugated with desmuramyl dipeptide, benzyl ester of L-alanyl-D-isoglutamine. Protection groups were removed in the final phase; acetate protections from mannose subunits and benzyl protections from D-isoglutamine. All synthesised compounds are structurally characterised with NMR spectroscopy, mass spectroscopy, with some of them also with IR spectroscopy