AtTrxh3, a Thioredoxin, Is Identified as an Abscisic AcidBinding Protein in Arabidopsis thaliana

Abscisic acid (ABA, 1) is a plant hormone that regulates various plant physiological processes such as seed developing and stress responses. The ABA signaling system has been elucidated; binding of ABA with PYL proteins triggers ABA signaling. We have previously reported a new method to isolate a protein targeted with a bioactive small molecule using a biotin linker with alkyne and amino groups, a protein cross-linker, and a bioactive small molecule with an azido group (azido probe). This method was used to identify the unknown ABA binding protein of Arabidopsis thaliana. As a result, AtTrxh3, a thioredoxin, was isolated as an ABA binding protein. Our developed method can be applied to the identification of binding proteins of bioactive compounds.

An efficient and practical chemo-enzymatic route to (3R,3aR,6R,6aR)-hexahydrofuro[3,2-b]furan-6-amino-3-ol (6-aminoisomannide) from renewable sources

The synthesis of 6-aminoisomannide is easily achieved starting from the renewable, inexpensive and commercially available isosorbide, in 66% overall yield. A biocatalysed highly regioselective acetylation of the 3-endo hydroxyl group of isosorbide was followed by the stereospecific interconversion of the 6-exo hydroxyl group into azido group, through reaction with trifluoromethanesulfonic anhydride followed by nucleophilic displacement of the triflate group by sodium azide. Finally, reduction of the azido group and deacetylation of the 3-hydroxy group were performed one pot by using LiAlH4.

Iron-Catalysed Remote C(sp3)-H Azidation of O-Acyl Oximes and N -Acyloxy Imidates

The azido group occupies an important position in modern organic chemistry, broadly used as amine surrogates and as anchors in bioconjugation. Despite their importance, examples of selective direct azidation of inert C(sp3)–H bonds remain limited and often require strong oxidative conditions. Herein, we highlight the use of O-acyl oximes and N-acyloxy imidates as directing groups for the selective iron-catalysed azidation of C(sp3)–H bond with trimethylsilyl azide, giving access to various γ-azido ketones and β-azido alcohols in moderate to excellent yields. The iron catalyst is assumed to play a dual role in these catalytic processes: as a reductant to generate the reactive iminyl and imidate radicals, respectively, and as a redox centre to mediate the azido transfer to the translocated carbon radical.

Nucleophilic transformations of azido-containing carbonyl compounds via protection of azido group

Nucleophilic transformations of azido-containing carbonyl compounds are disclosed. The phosphazide formation from azides and di(tert-butyl)(4-(dimethylamino)phenyl)phosphine (Amphos) enabled transformations of carbonyl groups with nucleophiles such as lithium aluminum hydride and organometallic...

Azidation of Partially Protected Carbohydrate Derivatives: Efficient Suppression of Acyl Migration

Although azidation by nucleophilic substitution is widely used in organic chemistry, it has a limitation for partially protected carbohydrate derivatives under typical reaction conditions used for azidation (heating with NaN3, phase-transfer catalyst (optional), DMF or DMSO) as it can cause substantial migration (70%) of O-acyl protective groups. Several approaches, including the use of a temporary protective group for the unprotected hydroxyl group, to avoid acyl migration have been compared. Addition of excess of ethyl trifluroacetate effectively suppressed benzoyl migration but inhibited substitution of the chlorine atom with the azido group. The most robust procedure involved addition of excess n-butyl formate to the reaction mixture. When this protocol was followed, migration of benzoyl groups in lactose derivatives with free hydroxy group at C-3′ or C-4′ was reduced to 4%, with the yield of the target, partially protected derivatives with an azido group in the aglycone approaching 92%.

Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-ʟ-arabinose

The incorporation of basic substituents into the structurally conserved domains of cell wall lipopolysaccharides has been identified as a major mechanism contributing to antimicrobial resistance of Gram-negative pathogenic bacteria. Inhibition of the corresponding enzymatic steps, specifically the transfer of 4-amino-4-deoxy-ʟ-arabinose, would thus restore the activity of cationic antimicrobial peptides and several antimicrobial drugs. C-glycosidically-linked phospholipid derivatives of 4-amino-4-deoxy-ʟ-arabinose have been prepared as hydrolytically stable and chain-shortened analogues of the native undecaprenyl donor. The C-phosphonate unit was installed via a Wittig reaction of benzyl-protected 1,5-arabinonic acid lactone with the lithium salt of dimethyl methylphosphonate followed by an elimination step of the resulting hemiketal, leading to the corresponding exo- and endo-glycal derivatives. The ensuing selective monodemethylation and hydrogenolysis of the benzyl groups and reduction of the 4-azido group gave the α-ʟ-anomeric arabino- and ribo-configured methyl phosphonate esters. In addition, the monomethyl phosphonate glycal intermediates were converted into n-octyl derivatives followed by subsequent selective removal of the methyl phosphonate ester group and hydrogenation to give the octylphosphono derivatives. These intermediates will be of value for their future conversion into transition state analogues as well as for the introduction of various lipid extensions at the anomeric phosphonate moiety.

Copresentation of BMP-6 and RGD Ligands Enhances Cell Adhesion and BMP-Mediated Signaling

We report on the covalent immobilization of bone morphogenetic protein 6 (BMP-6) and its co-presentation with integrin ligands on a nanopatterned platform to study cell adhesion and signaling responses which regulate the transdifferentiation of myoblasts into osteogenic cells. To immobilize BMP-6, the heterobifunctional linker MU-NHS is coupled to amine residues of the growth factor; this prevents its internalization while ensuring that its biological activity is maintained. Additionally, to allow cells to adhere to such platform and study signaling events arising from the contact to the surface, we used click-chemistry to immobilize cyclic-RGD carrying an azido group reacting with PEG-alkyne spacers via copper-catalyzed 1,3-dipolar cycloaddition. We show that the copresentation of BMP-6 and RGD favors focal adhesion formation and promotes Smad 1/5/8 phosphorylation. When presented in low amounts, BMP-6 added to culture media of cells adhering to the RGD ligands is less effective than BMP-6 immobilized on the surfaces in inducing Smad complex activation and in inhibiting myotube formation. Our results suggest that a local control of ligand density and cell signaling is crucial for modulating cell response.

Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-L-arabinose

Incorporation of basic substituents into the structurally conserved domains of cell-wall lipopolysaccharides has been identified as a major mechanism contributing to antimicrobial resistance of Gram-negative pathogenic bacteria. Inhibition of the corresponding enzymatic steps, specifically the transfer of 4-amino-4-deoxy-L-arabinose would thus restore the activity of cationic antimicrobial peptides and several antimicrobial drugs. C-glycosidically linked phospholipid derivatives of 4-amino-4-deoxy-L-arabinose have been prepared as hydrolytically stable and chain-shortened analogues of the native undecaprenyldonor. The C-phosphonate unit was installed via a Wittig-type reaction of benzyl-protected 1,5-arabinonic acid lactone with the lithium salt of dimethyl methylphosphonate followed by an elimination step of the resulting hemiketal leading to the corresponding exo- and endo-glycal derivatives. The ensuing selective mono-demethylation and hydrogenolysis of the benzyl groups and reduction of the 4-azido group gave the α-L-anomeric arabino- and ribo-configured methyl phosphonate esters. In addition, the monomethyl phosphonate glycal intermediates were converted into n-octyl derivatives followed by subsequent selective removal of the methyl phosphonate ester group and hydrogenation to give the octyl-phosphono derivatives. These intermediates thus will be of value for future conversion into transition state analogues as well as for introduction of various lipid extensions at the anomeric phosphonate moiety.