The role of local steric influences on the solution conformation and the biological activity of the H-type II blood group determinant 1 has been evaluated using structurally modified trisaccharides 2-4 and their corresponding C1-substituted C-glycosides 5-8 as conformational models. The preference of the C-glycosidic bond to adopt the gauche "exo-anomeric" conformation and the removal of destabilizing 1,3-diaxial-like interactions on the C-aglyconic bond have been used to create predictable conformational characteristics in C-trisaccharides 5-8. Vicinal coupling constants from 'H NMR spectroscopy and 2D NOESY spectroscopy demonstrate that structural modifications in the C-trisaccharides result in large changes in their conformational preferences. To test the impact of solution conformation on receptor-ligand recognition, the affinities of compounds 1-8 toward the lectin I of Ulex europaeus (UEA-I) have been investigated using a quantitative binding assay. The binding affinities of the H-type 11 trisaccharide 1 and the corresponding carbon analog 5 are virtually identical. The activities of the structurally modified C-trisaccharides 6-8 decrease sharply relative to the unmodified C-trisaccharide 5, correlating conformation to binding affinity. A parallel gradient in binding affinity is observed for the 0-trisaccharides 1-4. The selectivity of UEA-I for epitopes 1-8 validates the assumption that its receptor site largely defines a bound conformation for the substrates, and establishes that the conformational behavior of 0-glycosides such as 1-4 is similar to that of C-glycosides such as 5-8. IntroductionThe growing body of evidence that oligosaccharides play vital roles in intercellular communication and cell-mediated processes has been accompanied by a commensurate surge of interest in carbohydrates.' Oligosaccharide solution conformation and macromolecular carbohydrate recognition have both become important topics of research. Stoichiometric binding of carbohydrate ligands by antibodies and lectins has been characterized thus far by (1) polar interactions and key hydrogen bonds? (2) complementary hydrophilichydrophobic domains on the ligand and receptor site,3 and (3) thermodynamic parameters optimizing hydrogen bond networks among the carbohydrate, the protein, and interstitial water molecules? Less well understood is the role of ligand molecular shape in protein-sugar interactions. Manipulation of an oligosaccharide's conformational bias through the modification of steric influences could in principle result in a more tightly binding ligand.5 Some attempts have been made to explore this issue in terms of conformational

The amyloid-β peptide (Aβ)—in particular, the 42–amino acid form, Aβ1-42—is thought to play a key role in the pathogenesis of Alzheimer’s disease (AD). Thus, several therapeutic modalities aiming to inhibit Aβ synthesis or increase the clearance of Aβ have entered clinical trials, including γ-secretase inhibitors, anti-Aβ antibodies, and amyloid-β precursor protein cleaving enzyme inhibitors. A unique class of small molecules, γ-secretase modulators (GSMs), selectively reduce Aβ1-42 production, and may also decrease Aβ1-40 while simultaneously increasing one or more shorter Aβ peptides, such as Aβ1-38 and Aβ1-37. GSMs are particularly attractive because they do not alter the total amount of Aβ peptides produced by γ-secretase activity; they spare the processing of other γ-secretase substrates, such as Notch; and they do not cause accumulation of the potentially toxic processing intermediate, β-C-terminal fragment. This report describes the translation of pharmacological activity across species for two novel GSMs, (S)-7-(4-fluorophenyl)-N2-(3-methoxy-4-(3-methyl-1H-1,2,4-triazol-1-yl)phenyl)-N4-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine-2,4-diamine (BMS-932481) and (S,Z)-17-(4-chloro-2-fluorophenyl)-34-(3-methyl-1H-1,2,4-triazol-1-yl)-16,17-dihydro-15H-4-oxa-2,9-diaza-1(2,4)-cyclopenta[d]pyrimidina-3(1,3)-benzenacyclononaphan-6-ene (BMS-986133). These GSMs are highly potent in vitro, exhibit dose- and time-dependent activity in vivo, and have consistent levels of pharmacological effect across rats, dogs, monkeys, and human subjects. In rats, the two GSMs exhibit similar pharmacokinetics/pharmacodynamics between the brain and cerebrospinal fluid. In all species, GSM treatment decreased Aβ1-42 and Aβ1-40 levels while increasing Aβ1-38 and Aβ1-37 by a corresponding amount. Thus, the GSM mechanism and central activity translate across preclinical species and humans, thereby validating this therapeutic modality for potential utility in AD.

Macrocyclic peptides containing N-alkylated amino acids have emerged as a promising therapeutic modality, capable of modulating protein-protein interactions and an intracellular delivery of hydrophilic payloads. While multichannel automated solid-phase peptide synthesis (SPPS) is a practical approach for peptide synthesis, the requirement for slow and inefficient chromatographic purification of the product peptides is a significant limitation to exploring these novel compounds. Herein, we invent a "catch-release" strategy for the nonchromatographic purification of macrocyclic peptides. A traceless catch process is enabled by the invention of a dual-functionalized N-terminal acetate analogue, which serves as a handle for capture onto a purification resin and as a leaving group for macrocyclization. Displacement by a C-terminal nucleophilic side chain thus releases the desired macrocycle from the purification resin. By design, this catch/release process is a logic test for the presence of the key components required for cyclization, thus removing impurities which lack the required functionality, such as common classes of peptide impurities, including hydrolysis fragments and truncated sequences. The method was shown to be highly effective with three libraries of macrocyclic peptides, containing macrocycles of 5-20 amino acids, with either thioether- or amine-based macrocyclic linkages; in this latter class, the reported method represents an enabling technology. In all cases, the catch-release protocol afforded significant enrichment of the target peptides purity, in many cases completely obviating the need for chromatography. Importantly, we have adapted this process for automation on a standard multichannel peptide synthesizer, achieving an efficient and completely integrated synthesis and purification platform for the preparation of these important molecules.

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