A Novel Domino Reaction: Cyclization of Alkynyl Sulfides by Reaction with IPy2BF4

Formation of polycyclic structures within a few minutes: The intramolecular cyclization of diynes, activated by a benzenesulfenyl substituent, upon reaction with IPy₂BF₄ proceeds as an efficient exo–endo coupling. A subsequent novel Friedel–Crafts-like ring closure provides the product [Eq. (1)]. Thus, intra- and intermolecular cyclizations can be carried out.     

Directed Evolution of an Iron(II)- and α-Ketoglutarate-Dependent Dioxygenase for Site-Selective Azidation of Unactivated Aliphatic C−H Bonds**

Fe^II- and α-ketoglutarate-dependent halogenases and oxygenases can catalyze site-selective functionalization of C−H bonds via a variety of C−X bond forming reactions, but achieving high chemoselectivity for functionalization using non-native functional groups remains rare. The current study shows that directed evolution can be used to engineer variants of the dioxygenase SadX that address this challenge. Site-selective azidation of succinylated amino acids and a succinylated amine was achieved as a result of mutations throughout the SadX structure. The installed azide group was reduced to a primary amine, and the succinyl group required for azidation was enzymatically cleaved to provide the corresponding amine. These results provide a promising starting point for evolving additional SadX variants with activity on structurally distinct substrates and for enabling enzymatic C−H functionalization with other non-native functional groups.     

Polycaprolactone based biodegradable polyurethanes

Two series of segmented polyurethanes were prepared with systematic variation in soft and hard segment length. The soft segment was constituted by polycaprolactone (PCL) blocks of molecular masses 530 or 2000 and the hard segment (HS) by urethane blocks, in a concentration that varied from 12% to 44% in weight of the whole polyurethane. Morphological analyses indicated that the amount of crystallinity of copolymers was strongly dependent on the PCL molar mass and hard segment content. The copolymers with longer PCL soft segments (Mn=2000) were semicrystalline, but those with shorter PCL segment (Mn=530) were unable to crystallize. The primary factor affectingthe biodegradability of copolymers as evaluated by Sturm tests was the extent of the phase separation, and that the segmental blending of the less biodegradable polyurethane (HS) blocks with PCL in the amorphous phase had a critical unfavorable consequence, which may be attributed to the size of the accessible area by microorganisms.