Spectroscopic studies of oligomers containing 2,5-trans furanoid sugar amino acids

Synthesis and conformational analysis of linear homo- and heterooligomers from novel 2-C-branched sugar amino acids (SAAs)

Sugar amino acids (SAAs), as biologically interesting structures bearing both amino and carboxylic acid functional groups represent an important class of multifunctional building blocks. In this study, we develop an easy access to novel SAAs in only three steps starting from nitro compounds in high yields in analytically pure form, easily available by ceric (IV) mediated radical additions. Such novel SAAs have been applied in the assembly of total nine carbopeptoids with the form of linear homo- and heterooligomers for the structural investigations employing circular dichroism (CD) spectroscopy, which suggest that the carbopeptoids emerge a well-extended, left (or right)-handed conformation similar to polyproline II (PPII) helices. NMR studies also clearly demonstrated the presence of ordered secondary structural elements. 2D-ROESY spectra were acquired to identify ⁱ⁺¹ NH ↔  ⁱ C ₁ H, ⁱ C ₂ H correlations which support the conformational analysis of tetramers by CD spectroscopy. These findings provide interesting information of SAAs and their oligomers as potential scaffolds for discovering new drugs and materials.

C-3 branched δ-3,5-cis- and trans-THF sugar amino acids: synthesis of the first generation of branched homooligomers

This article describes the efficient synthesis of the first generation of branched sugar amino acid (SAA) oligomers in solution phase via two main routes: by the use of a standard coupling reagent and via the use of active ester intermediates. Benzyl-protected dimeric carbopeptoid and methyl-protected dimeric and tetrameric, hexameric and octameric carbopeptoids were obtained from a branched δ-3,5-trans-tetrahydrofuran (THF) SAA and methyl-protected dimeric and tetrameric carbopeptoids were synthesised from a branched δ-3,5-cis-THF SAA. These systems are of interest because of their potential to display foldameric properties reminiscent of those observed in α-peptides and proteins. Amongst their many uses, foldamers provide simpler models in the study of the factors which induce the folding and unfolding of proteins and, ultimately, potential insights into their functioning.

Penta-fluoro-phenyl (3R,4R,5S)-5-{[(3R,4R,5S)-5-azido-methyl-3,4-dimeth-oxy-2,3,4,5-tetra-hydro-furan-3-carboxamido]-meth-yl}-3,4-dimeth-oxy-2,3,4,5-tetra-hydro-furan-3-carboxyl-ate

The title compound, C(22)H(25)F(5)N(4)O(9), is a stable penta-fluoro-phenyl ester inter-mediate in the synthesis of novel homo-oligomeric structures containing branched carbon chains. The structure is epimeric to the previously characterized dimeric penta-fluoro-phenyl ester with stereochemistry (3R,4R,5R), which was synthesized using d-ribose as starting material. The crystal structure of the title mol-ecule removes any ambiguities arising from the relative stereochemistries of the six chiral centres. Two hydrogen bonds, bifurcating from the NH group, stabilize the crystal: one intra-molecular and one inter-molecular, both involving O atoms of the meth-oxy groups. The asymmetric unit contains two independent mol-ecules not related by any pseudo-symmetry operators. The major conformational differences are localized, leading to one mol-ecule being extended compared to the other. The collected crystal was twinned (twin ratio is 0.939:0.061), and the azide group is positionally disordered over two positions in one mol-ecule [occupancy ratio 0.511 (18):0.489 (18)].

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

Oligosaccharides are currently recognised as having functions that influence the entire spectrum of cell activities. However, a distinct disadvantage of naturally occurring oligosaccharides is their metabolic instability in biological systems. Therefore, much effort has been spent in the past two decades on the development of feasible routes to carbohydrate mimetics which can compete with their O-glycosidic counterparts in cell surface adhesion, inhibit carbohydrate processing enzymes, and interfere in the biosynthesis of specific cell surface carbohydrates. Such oligosaccharide mimetics are potential therapeutic agents against HIV and other infections, against cancer, diabetes and other metabolic diseases. An efficient strategy to access this type of compounds is the replacement of the glycosidic linkage by amide or pseudoamide functions such as thiourea, urea and guanidine. In this review we summarise the advances over the last decade in the synthesis of oligosaccharide mimetics that possess amide and pseudoamide linkages, as well as studies focussing on their supramolecular and recognition properties.