John R. Naber

Palladium-catalyzed amination reactions in flow: overcoming the challenges of clogging via acoustic irradiation

A continuous-flow palladium-catalyzed amination reaction was made possible through efficient handling of solids via acoustic irradiation. Various diarylamines were obtained with reaction times ranging from 20 s to 10 min.

Augmentation of postswelling surgical sealant potential of adhesive hydrogels

Two-component hydrogels formed with star polyethylene glycol amine and linear dextran aldehyde polymers (PEG:dextran) show promise as tissue-specific surgical sealants. However, there is a significant loss of adhesion strength to soft tissues following PEG:dextran swelling, which may limit material ability to appose disjoined tissues and prevent leakage from surgical sites. We covalently incorporated the modified amino acid L-3,4-dihydroxyphenylalanine (L-DOPA) into PEG:dextran to enhance postswelling sealant performance. L-DOPA is an essential component of marine animal adhesive plaques and has been used to confer wet adhesion in synthetic materials. As both PEG:dextran cohesion and adhesion are mediated by aldehyde-amine interactions, L-DOPA side-groups make it a potent network modulator with potential to affect multiple material properties. Following 1-h submersion in aqueous media, PEG:dextran doped with 3 mM L-DOPA/M aldehyde on average swelled 50.3% less, had 287.4% greater stiffness, and had 53.6% greater functional adhesion strength compared to the neat hydrogel. Increased concentrations of L-DOPA up to 11 mM L-DOPA/M aldehyde similarly curtailed swelling and mitigated property loss with hydration, but sacrificed initial functional adhesion strength, material modulus, and biocompatibility. Taken together, these data support tailored L-DOPA conjugation as a promising approach to enhance the clinical performance of PEG:dextran sealants.

STILLE CROSS-COUPLING REACTIONS OF ARYL MESYLATES AND TOSYLATES USING A BIARYLPHOSPHINE BASED CATALYST SYSTEM.

A catalyst system for the Stille cross-coupling reactions of aryl mesylates and tosylates is reported. Using the combination of Pd(OAc)2, XPhos, and CsF in t-BuOH an array of aryl and heteroaryl sulfonates were successfully employed in these reactions. Morever, heteroarylstannanes, such as furyl, thiophenyl, and N-methylpyrrole, which are often prone to decomposition, were efficiently coupled under these conditions. Ortho-substitution on the stannane coupling partner was well tolerated; however, the presence of ortho substituents on the aryl sulfonates greatly reduced the proficiency of these reactions.