Is adamantane a suitable substituent to pre-organize the acid orientation in E-selectin antagonists?

The selectins play a key role in the inflammatory process, that is, the recruitment of leukocytes from blood vessels into inflamed tissue. Because excessive infiltration of leukocytes can induce acute or chronic reactions, the control of leukocyte extravasation is of great pharmaceutical interest. All physiological ligands of the selectins contain the tetrasaccharide epitope sialyl Lewis(x), which therefore became the lead structure in selectin antagonist research. Previous studies indicated that an important factor for the affinity of sLe(x) is the fact that in solution its pharmacophores are already conformationally pre-organized in the bioactive orientation. In mimics where the GlcNAc- and the NeuNAc-moieties of sLe(x) were replaced by (R,R)-cyclohexane-1,2-diol and (S)-cyclohexyllactic acid, respectively, an optimized pre-organization of the pharmacophores could be realized, leading to antagonists with improved affinities. To further optimize the pre-organization of the carboxylic acid, a pharmacophore essential for binding, the replacement of NeuNAc by bulky (R)- and (S)-adamantyl-lactic acid was studied. Although antagonist (S)-7 showed a slightly reduced affinity, the expected beneficial effect of the (S)-configuration at C-2 of the lactate could be confirmed.

Antagonists of the myelin-associated glycoprotein: a new class of tetrasaccharide mimics.

The tetrasaccharide substructure 1 of the ganglioside GQ1balpha shows a remarkable affinity for the myelin-associated glycoprotein (MAG). In the search for structurally simplified and pharmacokinetically improved mimics of 1, biphenyl was identified as a feasible replacement for the core disaccharide Galbeta(1-3)GalNAc according to saturation transfer difference (STD) NMR and molecular modeling investigations. Using Suzuki coupling, a convergent synthesis of the mimics was achieved. To optimize the yields of the coupling reactions, the catalytic effects of microwave irradiation and conventional heating were compared. The biological evaluation of mimics 3 and 4 was performed in a competitive target-based assay. It was found that the relative inhibitory potency (rIP) of antagonist 3 was clearly enhanced in comparison to the reference trisaccharide 2, despite the former having a much simpler structure. In addition to the improved synthetic feasibility, an increase of the partition coefficient between octanol and water (logP), and therefore a beneficial change in the pharmacokinetic properties of 3 and 4 was achieved.