A bicyclic peptide scaffold promotes phosphotyrosine mimicry and cellular uptake

While peptides are promising as probes and therapeutics, targeting intracellular proteins will require greater understanding of highly structured, cell-internalized scaffolds. We recently reported BC1, an 11-residue bicyclic peptide that inhibits the Src homology 2 (SH2) domain of growth factor receptor-bound protein 2 (Grb2). In this work, we describe the unique structural and cell uptake properties of BC1 and similar cyclic and bicyclic scaffolds. These constrained scaffolds are taken up by mammalian cells despite their net neutral or negative charges, while unconstrained analogs are not. The mechanism of uptake is shown to be energy-dependent and endocytic, but distinct from that of Tat. The solution structure of BC1 was investigated by NMR and MD simulations, which revealed discrete water-binding sites on BC1 that reduce exposure of backbone amides to bulk water. This represents an original and potentially general strategy for promoting cell uptake.     

A novel resolution of a pharmaceutically important bridged bicyclic ketone intermediate via selective enzymatic reduction with a commercially available ketoreductase

An efficient route to the pharmaceutically important (6S,9R)-11-oxo-5,6,7,8,9,10-hexahydro-6,9-methanobenzocyclooctene intermediate has been demonstrated via kinetic resolution of 11-oxo-5,6,7,8,9,10-hexahydro-6,9-methanobenzocyclooctene using a commercially available ketoreductase. Biocatalytics KRED 101 has been shown to selectively reduce the (6R,9S) enantiomer leaving behind the desired (6S,9R) enantiomer. This novel reaction is the first demonstration of a high yielding (44% versus 50% maximum theoretical yield) highly stereoselective (>99% ee) resolution of a bicyclic ketone, via enzymatic reduction using a commercially available ketoreductase, where the stereochemistry of the substrate is determined by a bridged ring system. Several challenges were overcome, including enhancing the selectivity of the enzyme by controlling temperature and increasing substrate solubility by employing a combination of cyclodextrin and organic co-solvent in the aqueous reaction system.     

Reaction of acrolein with 2'-deoxyadenosine and 9-ethyladenine--formation of cyclic adducts

Treatment of 2'-deoxyadenosine with acrolein at pH 4.6 in 37 degrees C affords unstable adducts containing either one or two fused ring systems where the hydroxypropano units are derived from acrolein. Since the use of 2'-deoxyadenosine resulted in the creation of at least four diastereoisomers for the adduct made up of two fused rings, therefore, for identification and assignment of the products, 9-ethyladenine was used instead as the starting material in the reaction. The products, 3E and 4E, were structurally characterised by UV, mass spectrometry and NMR spectroscopy.     

Investigation of 1,3-Dipolar Cycloaddition Reactions of Unsaturated Nitrones in Ionic Liquids

The effect of the media (achiral and chiral ionic liquids) on the stereochemistry of intramolecular 1,3-dipolar cycloaddition reactions of D-galactose-derived ω-unsaturated nitrones, leading to bicyclic isoxazolidines, has been investigated.     

Novel human adenosine receptor antagonists based on the 7-amino-thiazolo[5,4-d]pyrimidine scaffold. Structural investigations at the 2-, 5- and 7-positions to enhance affinity and tune selectivity

This paper describes the synthesis of novel 7-amino-thiazolo[5,4-d]pyrimidines bearing different substituents at positions 2, 5 and 7 of the thiazolopyrimidine scaffold. The synthesized compounds 2–27 were evaluated in radioligand binding (A₁, A_2A and A₃) and adenylyl cyclase activity (A_2B and A_2A) assays, in order to evaluate their affinity and potency at human adenosine receptor subtypes. The current study allowed us to support that affinity and selectivity of 7-amino-thiazolo[5,4-d]pyrimidine derivatives towards the adenosine receptor subtypes can be modulated by the nature of the groups attached at positions 2, 5 and 7 of the bicyclic scaffold. To rationalize the hypothetical binding mode of the newly synthesized compounds, we also performed docking calculations in human A_2A, A₁ and A₃ structures.     

Bicyclic Nucleoside Synthesis—A Photochemical Approach

The synthesis of a series of bicyclic nucleosides using photolytic ring-expansion of cyclobutanones is reported. The cyclobutanone precursors were prepared by [2+2] cycloaddition of a series of cyclic alkenes with chlorinated ketenes, derived from dichloro- and trichloroacetyl chloride. The synthesis of the nucleosides was achieved through photolysis of cyclobutanone precursors with 6-chloropurine by UV irradiation. The generality of this method was investigated and the absolute stereochemistry was assigned by NMR spectroscopy. The photoproducts demonstrated a marked preference for the 2′-exo conformation.     

Synthesis of 2′-O,4′-C-alkylene-bridged ribonucleosides and their evaluation as inhibitors of HCV NS5B polymerase

The synthesis of 2′-O,4′-C-methylene-bridged bicyclic guanine ribonucleosides bearing 2′-C-methyl or 5′-C-methyl modifications is described. Key to the successful installation of the methyl functionality in both cases was the use of a one-pot oxidation–Grignard procedure to avoid formation of the respective unreactive hydrates prior to alkylation. The 2′-C-methyl- and 5′-C-methyl-modified bicyclic guanosines were evaluated, along with the known uracil-, cytosine-, adenine-, guanine-LNA and guanine-ENA nucleosides, as potential antiviral agents and found to be inactive in the hepatitis C virus (HCV) cell-based replicon assay. Examination of the corresponding nucleoside triphosphates, however, against the purified HCV NS5B polymerase indicated that LNA-G and 2′-C-methyl-LNA-G are potent inhibitors of both 1b wild type and S282T mutant enzymes in vitro. Activity was further demonstrated for the LNA-G-triphosphate against HCV NS5B polymerase genotypes 1a, 2a, 3a and 4a. A phosphorylation by-pass prodrug strategy may be required to promote anti-HCV activity in the replicon assay.     

Stereospecific synthesis of a new class of compounds: bis-homoconduritol-A, -D, and -F

Bis-homoconduritol derivatives with conduritol-A, -D, and -F structures have been synthesized starting from cyclooctatetraene. The photooxygenation of trans-7,8-dibromo- and cis-7,8-dichlorobicyclo[4.2.0]octa-2,4-dienes afforded the bicyclic endoperoxides. Reduction of the endoperoxides with thiourea followed by acetylation gave the corresponding diacetates. The KMnO(4) oxidation and epoxidation of the diacetates followed by acetylation gave the tetraacetates. Removal of the halides either with zinc-dust or Na-anthracene followed by the ammonolysis of tetraacetates afforded the bis-homoconduritol derivatives in high yield.     

Bicyclic nucleoside analogues from D-glucose: synthesis of chiral as well as racemic 1,4-dioxepane ring-fused derivatives

The dioxepanofuranose derivatives 4 and 12, obtained through the cyclization of the 3-(2-hydroxyethyl) ether of a D-xylo-pentodialdose derivative, were appropriately functionalized and elaborated to the first examples of the new class of 3'-O and 5'-O-bicyclic nucleoside analogues 9, 10, and 14 with a fused seven-membered ring. Reactions carried out through the intermediacy of the D-xylo-pentodialdose derivative 5 yielded racemic products, while prior protection of the 4-formyl group (as in 7) before deprotection of the 1,2-hydroxyl groups led to optically active analogues.