3-Aza-6,8-dioxabicyclo[3.2.1]octane-7-carboxylic acids (named BTAa) derived from (R,R)-, (S,S)-, or meso-tartaric acid and natural (l), unnatural (d), or unusual α-amino acids are described as conformationally constrained dipeptide isosteres. The general strategy developed for their preparation has required the trasformation of the amino acids into the corresponding N-benzylamino alcohols, followed by the PyBroP-promoted condensation with the monomethyl ester of the suitable 2,3-di-O-isopropylidenetartaric acid. Oxidation of the hydroxy group to aldheyde and subsequent acid-catalyzed trans-acetalization with the two hydroxy groups of the tartaric acid moiety provided 3-aza-2-oxo-6,8-dioxabicyclo[3.2.1]octane-7-carboxylic acid methyl esters [named BTAa(O)] in good yield and, in most cases, as single enantiopure diastereoisomers. This strategy has been applied to the preparation of BTAa(O) starting from (R,R)-, (S,S)-, or meso-tartaric acid and glycine, l- and d-phenylalanine, l- and d-alanine, and (±)-phenylglycine. In the cases of glycine, l- and d-phenylalanine, and l- and d-alanine, the selective reduction by BH3·DMS of the amide group succeeding to the cyclization step, or the reduction of both amide and ester functions followed by reoxidation of the hydroxy to carboxylic group, provided in good yield the 3-aza-3-benzyl-6,8-dioxabicyclo[3.2.1]octane-7-carboxylic acids (or their methyl ester) BTAa, having the side chain of the amino acid precursors at position 4. The stability and rigidity of the bicyclic skeleton, the complete control of all the stereocenters, the possibility of introducing the side chains of l- or d-amino acids, and the demonstrated compatibility with the conditions required for solid-phase peptide synthesis make the BTAa compounds potential dipeptide isosteres useful for the synthesis of modified peptides.

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The embodiment of 4-aminoproline residues (Amp) into the arginine-glycine-aspartate (RGD) sequence led to the discovery of a novel class of high-affinity alpha Vbeta 3/alpha Vbeta 5 integrin binders [IC 50 h (alpha Vbeta 3) 0.03-5.12 nM; IC 50 h (alpha Vbeta 5) 0.88-154 nM]. A total of eight cyclopeptides of type cyclo-[-Arg-Gly-Asp-Amp-], 5- 12, were assembled by a standard solid-phase peptide synthesis protocol that involved the C2-carboxyl and C4-amino functionalities of the proline scaffolds, leaving the N (alpha)-nuclear site untouched. Functionalization of this vacant proline site with either alkyl or acyl substituents proved feasible, with significant benefit to the integrin binding capabilities of the ligands. Notably, six out of eight cyclopeptide inhibitors, 5- 7 and 9- 11, showed moderate yet significant selectivity toward the alpha Vbeta 3 receptor. The three-dimensional structure in water was determined by NMR techniques and molecular dynamics calculations. Docking studies to the X-ray crystal structure of the extracellular segment of integrin alpha Vbeta 3 complexed with reference compound 1 were also performed on selected analogues to highlight the structural features required for potent ligand binding affinity.

A click chemistry approach was applied for the discovery of triazole-based arginine-glycine-aspartate (RGD) mimetics by Cu(I)-catalyzed 1,3-dipolar alkyne-azide coupling reaction, which showed binding affinity properties toward α(v)β(3)/α(v)β(5) integrins. Biological assays showed compound 18 capable of binding α(v)β(3) integrin with nanomolar affinity according to a two-sites model, and molecular modeling studies revealed a peculiar π-stacking interaction between the triazole ring and Tyr178 side chain. Accordingly, compound 18 inhibited the adhesion of integrin-expressing human melanoma cells to RGD-containing proteins of the extracellular matrix, such as vitronectin, fibronectin, and osteopontin, and also angiogenesis in in vitro and in vivo experimental models. The relevant biological effects exerted by compound 18 suggest its potential application as an antiangiogenic agent in the diagnosis and therapy of tumors where α(v)β(3) integrin expression is up-regulated.

Over the last decade, Diversity-Oriented Synthesis (DOS) has become a new paradigm for developing large collections of structurally diverse small molecules as probes to investigate biological pathways, and to provide a larger array of the chemical space. Drug discovery and chemical biology are taking advantage of DOS approaches to exploit highly-diverse and complex molecular platforms, producing advances in both target and ligand discovery. In this view, carbohydrates are attractive building blocks for DOS libraries, due to their stereochemical diversity and high density of polar functional groups, thus offering many possibilities for chemical manipulation and scaffold decoration. This review will discuss research contributions and perspectives on the application of carbohydrate chemistry to explore the accessible chemical space through appendage, stereochemical and scaffold diversity.

The chemoinformatics analysis of fused, spiro, and bridged bicyclic acetals is instrumental for the DOS of natural product-inspired molecular collections.

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Free radical polymerization of both a-(trifluoromethy1)acrylic acid (TFMAA) and its methyl ester MTFMA is shown to be possible in the presence of bis(4-tert-butylcyclohexyl) peroxycarbonate (Percadox) as initiator and dioxane or THF as solvent. Also it is shown that copolymers of TFMAA with a-olefins (1-decene, 2-methyl-1-hexene) and of methyl a-(trifluoromethy1)acrylate (MTFMA) with vinyl ethers (butyl, 2-ethylhexyl, and menthyl vinyl ether) can be simply obtained with AIBN as initiator; these copolymers have a predominantly alternating structure.