Tri‐tert‐butyl 3‐oxo‐4‐oxa‐1,8,11‐triazaspiro[5.6]dodecane‐1,8,11‐triacetate

The title compound, C₂₆H₄₅N₃O₈, is a bicyclic molecule; the seven‐membered diazepane ring has a twisted‐chair conformation and the six‐membered morpholine ring has a boat conformation.     

Esters as Radical Acceptors: β‐NHC‐Borylalkenyl Radicals Induce Lactonization by C−C Bond Formation/Cleavage on Esters

Substituted propargyl acetates are converted into 4‐boryl‐2(5H)‐furanones upon thermolysis in the presence of an N‐heterocyclic carbene borane (NHC‐borane) and di‐tert‐butyl peroxide. The acetyl methyl group is lost during the reaction as methane. Evidence suggests that the reaction proceeds by a sequence of radical events including: 1) addition of an NHC‐boryl radical to the triple bond; 2) cyclization of the resultant β‐borylalkenyl radical to the ester carbonyl group; 3) β‐scission of the so‐formed alkoxy radical to provide the 4‐boryl‐2(5H)‐furanone and a methyl radical; and 4) hydrogen abstraction from the NHC‐borane to return the initial NHC‐boryl radical and methane.     

Synthesis and crystal structure of 4-amino-3-fluorophenylboronic acid

4-Amino-3-fluorophenyl boronic acid has been synthesized from 4-bromo-2-fluoroaniline by protecting the amine group and then carrying out a lithium-bromine exchange, followed by addition of trimethyl borate and then acidic hydrolysis. We obtained a 47% yield. We also measured the X-ray crystal structure. This derivative has a relatively low boronic acid pK_a value of 7.8 when acetylated or attached to acrylamide hydrogels. It also contains a pendant amine which facilitates attachment to polymers, for example. We are using this compound to construct glucose sensing materials that operates at the physiological pH of bodily fluids.     

Fluorous Synthesis of Hydantoin-, Piperazinedione-, and Benzodiazepinedione-Fused Tricyclic and Tetracyclic Ring Systems

Fluorous proline derivatives generated from one-pot, three-component [3+2] cycloaddition of azomethine ylides are employed for different post-condensation reactions to form hydantoin-, piperazinedione-, and benzodiazepinedione-fused tricyclic and tetracyclic ring systems. The high synthetic efficiency is achieved by conducting fast microwave reactions and easy fluorous-solid phase extractions for reaction mixture purifications. Methods developed for these novel drug-like heterocyclic compounds can be applied to diversity-oriented library synthesis.     

Synthesis and binding studies of Alzheimer ligands on solid support

Aminopyrazole derivatives constitute the first class of nonpeptidic rationally designed beta-sheet ligands. Here we describe a double solid-phase protocol for both synthesis and affinity testing. The presented solid-phase synthesis of four types of hybrid compounds relies on the Fmoc strategy and circumvents subsequent HPLC purification by precipitating the final product from organic solution in pure form. Hexa- and octapeptide pendants with internal di- and tetrapeptide bridges are now amenable in high yields to combinatorial synthesis of compound libraries for high-throughput screening purposes. Solid-phase peptide synthesis (SPPS) on an acid-resistant PAM allows us, after PMB deprotection, to subject the free aminopyrazole binding sites in an immobilized state to on-bead assays with fluorescence-labeled peptides. From the fluorescence emission intensity decrease, individual binding constants can be calculated via reference curves by simple application of the law of mass action. Gratifyingly, host/guest complexation can be monitored quantitatively even for those ligands, which are almost insoluble in water.     

N6‐Furfuryladenine (kinetin) hydrochloride

In the title compound, N⁶‐furfuryl­adenin‐3‐ium chloride, C₁₀H₁₀N₅O⁺·Cl⁻, the adenine moiety exists as the N3‐protonated N7–H tautomer. The orientation of the N6 substituent (furfuryl moiety) is distal to the imidazole ring of the adenine base. The dihedral angle between the adenine plane and the furfuryl ring plane is 76.1 (2)°. Three N—H⋯Cl hydrogen bonds are responsible for the formation of a supramolecular chain‐like pattern. These supramolecular chains are interconnected by C—H⋯Cl hydrogen bonds to form a hydrogen‐bonded sheet and a three‐dimensional hydrogen‐bonded network.     

Supramolecular self-assembly based on directed hydrogen bonding

A series of hydrogen-bonding monomers has been constructed and shown to form discrete aggregates both in solution and in the solid state.     

Substitution reactions at tetracoordinate boron: synthesis of N-heterocyclic carbene boranes with boron-heteroatom bonds

Boryl halide, carboxylate and sulfonate complexes of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (dipp-Imd-BH(2)X, X = halide or sulfonate) have been prepared from the parent borane dipp-Imd-BH(3) by (1) substitution reactions with R-X (X = halide or sulfonate), (2) reactions with electrophiles (like I(2) or NIS), or (3) acid/base reactions with HX (provided that HX has a pK(a) of about 2 or less). Dipp-Imd-BH(2)I is most conveniently prepared by reaction with diiodine while dipp-Imd-BH(2)OTf is best prepared by reaction with triflic acid. These and other less reactive complexes behave as electrophiles and can be substituted by a wide range of heteroatom nucleophiles including halides, thiolates and other sulfur-based nucleophiles, isocyanate, azide, nitrite, and cyanide. The resulting products are remarkably stable, and many have been characterized by X-ray crystallography. Several are members of very rare classes of functionalized boron compounds (boron azide, nitro compound, nitrous ester, etc.).