Variation in the Structure and Activity of Commercial Palladium on Carbon Catalysts

<p>Palladium catalysed hydrogenolysis is often the final step in challenging natural product total synthesis and a key step in industrial processes towards fine chemicals. Here we demonstrate that there is wide variability in quality of commercial sources of palladium on carbon (Pd/C), which results in differences in selectivity, reaction times, and yields. This is established through a combination of XRD, XPS, BET and TEM analysis, this will serve as a template for others to quickly identify a high-quality source of Pd/C catalyst — meaning less time spent on time consuming reaction optimisation studies. Key indicators of a high-quality catalyst include: small particle sizes, large surface area, and the presence of both Pd⁰ and Pd²⁺active species (not present in all commercial sources). Further this work will enable the design and synthesis of new high-quality Pd/C catalysts.</p>

Variation in the Structure and Activity of Commercial Palladium on Carbon Catalysts

<p>Palladium catalysed hydrogenolysis is often the final step in challenging natural product total synthesis and a key step in industrial processes towards fine chemicals. Here we demonstrate that there is wide variability in quality of commercial sources of palladium on carbon (Pd/C), which results in differences in selectivity, reaction times, and yields. This is established through a combination of XRD, XPS, BET and TEM analysis, this will serve as a template for others to quickly identify a high-quality source of Pd/C catalyst — meaning less time spent on time consuming reaction optimisation studies. Key indicators of a high-quality catalyst include: small particle sizes, large surface area, and the presence of both Pd⁰ and Pd²⁺active species (not present in all commercial sources). Further this work will enable the design and synthesis of new high-quality Pd/C catalysts.</p>

Clues to a Pd/C catalyst’s efficiency can be found on its surface: Identification of an efficient catalyst for the global hydrogenolysis of ether protecting groups

<p>We report insights into our observations of the wide variability in quality of palladium catalyst from different suppliers, finding the fundamental differences can be rationalized through a combination of XRD, XPS, and TEM analysis, offering the possibility to predict a catalysts performance prior to the use of valuable synthetic material and save time consuming efforts to identify high quality palladium on carbon catalysts. The synthetic glycan accessed in this study will allow further steps towards the development of semisynthetic vaccines against cryptococcal infections.</p>

O-Benzylhydroxylamine (BHA) as a Cleavable Tag for Isolation and Purification of Reducing Glycans

Glycoscience has been recognized as an important area in biomedical research. Currently, a major obstacle for glycoscience study is the lack of diverse, biomedically relevant, and complex glycans in quantities sufficient for exploring their structural and functional aspects. Complementary to chemoenzymatic synthesis, natural glycans could serve as a great source of biomedically relevant glycans if they are available in sufficient quantities. We have recently developed oxidative release of natural glycans (ORNG) for large-scale release of N-glycans as free reducing glycans. While free reducing glycans can be readily derivatized with ultraviolet or fluorescent tags for high-performance liquid chromatography (HPLC) and mass spectrometry (MS) analysis, it is difficult to remove tags for the regeneration of free reducing glycans without affecting the structural integrity of glycans. To address this inconvenience, we explored the use of a cleavable tag, O-benzylhydroxylamine (BHA). Free reducing glycans are easily and efficiently labeled with BHA under mild conditions, enabling UV detection during HPLC purification. Individual glycan–BHA conjugates can then be separated using multidimensional HPLC and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and MS/MS. The BHA tag can then be easily removed by palladium-on-carbon (Pd/C)-catalyzed hydrogenation to efficiently regenerate free reducing glycans with little effect on glycan structures. This procedure provides a simple and straightforward way to tag free reducing glycans for purification at a preparative scale using multidimensional HPLC and subsequently recover purified free reducing glycans.

Direct C–H bond activation: palladium-on-carbon as a reusable heterogeneous catalyst for C-2 arylation of indoles with arylboronic acids

We report a methodology for exclusive C-2 arylated indoles without the aid of any ligand or directing group in air.