Aminomethylhydroxylation of alkenes: Exploitation in the synthesis of scaffolds for small molecule libraries.

The application of [4+2] cycloadditions between alkenes and an N-benzoyl iminium species, generated in situ under acidic conditions, is described in the synthesis of diverse molecular scaffolds. The key reaction led to the formation of cyclic imidates in good yield and with high regioselectivity. It was demonstrated that the cyclic imidates may be readily converted into 1,3-amino alcohols. Incorporation of orthogonally-reactive functionality, such as aryl and alkyl bromides, into the cycloaddition substrates enabled the synthesis of additional scaffolds. For one scaffold, the synthesis of exemplar screening compounds was undertaken to demonstrate potential value in small molecule library production.

1-Ethoxyethylidene, a new group for the stepwise SPPS of aminooxyacetic acid containing peptides.

For more than a decade, the oxime ether ligation has proven to be one of the most efficient technique for the preparation of various peptide conjugates. However, despite numerous reports, the preparation of aminooxy-containing peptides is still hampered by N-overacylation of the NH-O function either during its incorporation or through the peptide-chain elongation. This restricts the introduction of protected-NH-O function at the last acylation step and prevents the use of standard solid-phase peptide synthesis (SPPS) procedures for the preparation of more complex aminooxy-peptides. We have studied the coupling of modified Fmoc-lysine containing either N-Boc- or N,N'-bis-Boc-protected aminooxyacetic acids (Aoa) during the elongation of the peptide chain and found that none of them is adequate. To circumvent this limitation, we propose to protect the Aoa moiety with a 1-ethoxyethylidene group (Eei) to provide 2-(1-ethoxyethylideneaminooxy)acetic acid building block. We showed that the Eei group is fully compatible with standard SPPS conditions and safely allows the multiple incorporation of the aminooxy functionality into the growing peptide. Since Eei-protected Aoa remains as flexible as normal amino acids in peptide synthesis, it may become the rule for the straightforward preparation of aminooxy peptides.

The relative orientation of the lipid and carbohydrate moieties of lipochitooligosaccharides related to nodulation factors depends on lipid chain saturation.

Lipochitooligosaccharides (LCOs) signal the symbiosis of rhizobia with legumes and the formation of nitrogen-fixing root nodules. LCOs 1 and 2 share identical tetrasaccharide scaffolds but different lipid moieties (1, LCO-IV(C16:1[9Z], SNa) and , LCO-IV(C16:2[2E,9Z], SNa)). The conformational behaviors of both LCOs were studied by molecular modeling and NMR. Modeling predicts that a small lipid modification would result in a different relative orientation of the lipid and tetrasaccharide moieties. Diffusion ordered spectroscopy reports that both LCOs form small aggregates above 1 mM. Nuclear Overhauser spectroscopy (NOESY) data, collected under monomeric conditions, reveals lipid-carbohydrate contacts only for 1, in agreement with the modeling data. The distinct molecular structures of 1 and 2 have the potential to contribute to their selective binding by legume proteins.

Diffusion ordered spectroscopy as a complement to size exclusion chromatography in oligosaccharide analysis.

A series of N-acetyl-chitooligosaccharides (GlcNAc)(1-6) have been studied by a nuclear magnetic resonance (NMR) method, diffusion ordered spectroscopy (DOSY). DOSY has also been applied to two additional synthetic related oligosaccharides [GlcNH(2)-(GlcNAc)(4) and GlcNH(2)-(GlcNAc)(2)-GlcNAcSO(3)Na]. A plot of the log of the determined diffusion coefficients (logD) of (GlcNAc)(n) versus the log of molecular weight was linear (6 points, R(2) = 0.995). The molecular weights of the two synthetic chitin derivatives could be estimated to within 10% error. The processed NMR data of all the chitooligosaccharides was also plotted in a polyacrylamide gel-like format to aid visual interpretation. Moreover, the logD value of the NMR signal resonances of a chitin-binding protein (hevein) changed as a function of a given titrated ligand, (GlcNAc)(6). Evidence for a 2:1 hevein:(GlcNAc)(6) complex is detected by DOSY at high hevein:(GlcNAc)(6) ratios. This data is consistent with published analytical ultracentrifugation and isothermal titration calorimetry data. A 1:1 complex is preferred at higher ligand concentrations. DOSY can complement size exclusion chromatography in carbohydrate research with the advantage that oligosaccharides are more readily detected by NMR.