Expeditious chemical synthesis of xylomannans disproves the proposed antifreeze activities.

Cold-adapted species are able to generate cryoprotective proteins and glycoproteins to prevent freezing damage. The [→4)-ß-D-Manp-(1→4)-ß-D-Xylp-(1→] n xylomannan from the Alaska beetle Upis ceramboides was disclosed by Walters and co-workers in 2009 as the first glycan-based antifreeze agent, which was later reported to be found in diverse taxa. Here, we report the rapid synthesis of four types of xylomannans, including the proposed antifreeze xylomannan up to a 64-mer (Type I), the regioisomeric [→3)-ß-D-Manp-(1→4)-ß-D-Xylp-(1→] n 16-mer (Type II), the diastereomeric [→4)-ß-L-Manp-(1→4)-ß-D-Xylp-(1→] n 16-mer (Type III) and the block-wise [→4)-ß-D-Manp-(1→] m [→4)-ß-D-Xylp-(1→] n 32-mer (Type IV), by employing a strategic iterative exponential glycan growth (IEGG) process. The nuclear magnetic resonance spectral data of the alleged natural xylomannan are in accordance only to those of the block-wise Type IV glycan and none of these synthetic xylomannans has been found to be capable of inducing thermal hysteresis. These results disprove the previous reports about the natural occurrence of antifreeze xylomannans.

OMS-2-Supported Cu Hydroxide-Catalyzed Benzoxazoles Synthesis from Catechols and Amines via Domino Oxidation Process at Room Temperature.

In the presence of manganese oxide octahedral molecular sieve (OMS-2) supported copper hydroxide Cu(OH)x/OMS-2, aerobic synthesis of benzoxazoles from catechols and amines via domino oxidation/cyclization at room temperature is achieved. This heterogeneous benzoxazoles synthesis initiated by the efficient oxidation of catechols over Cu(OH)x/OMS-2 tolerates a variety of substrates, especially amines containing sensitive groups (hydroxyl, cyano, amino, vinyl, ethynyl, ester, and even acetyl groups) and heterocycles, which affords functionalized benzoxazoles in good to excellent yields by employing low catalyst loading (2 mol % Cu). The characterization and plausible catalytic mechanism of Cu(OH)x/OMS-2 are described. The notable features of our catalytic protocol such as the use of air as the benign oxidant and EtOH as the solvent, mild conditions, ease of product separation, being scalable up to the gram level, and superior reusability of catalyst (up to 10 cycles) make it more practical and environmentally friendly for organic synthesis.