Herein, an indazolyl-pyridinyl-triazole ligand was synthesized and its iridium complex supported on hydrotalcite was characterized via X-ray power diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) spectroscopy and transmission electron microscopy (TEM). This new heterogeneous catalyst bearing the unsymmetrical indazolyl-pyridinyl-triazole ligand exhibits high catalytic activity in water. Both functionalized amines and imines were obtained from the challenging selective reaction of benzylamines with arylamines through transfer hydrogenation and dehydrogenation under clean conditions. In particular, it was observed that this catalyst system showed good recovery performance in water. Mechanistic studies showed that this transformation occurs via amine dehydrogenation, hydrolysis and condensation processes. The direct capture of the reaction intermediate provides sufficient proof for this process.

Where does Au coordinate to N-(2-pyridiyl)benzotriazole? Here, pyridyltriazole gold(I) complexes were synthesized, whereby it was revealed that the triazole part coordinated to gold(I). Compared to the Ph₃PAuCl/AgOTf catalyst, pyridyltriazole gold(I) complexes proved to be an efficient pre-catalyst for the most challenging gold-catalyzed borrowing hydrogen reaction and dehydrogenation of alcohols and amines, which provided an efficient method to selectively synthesize imines, substituted amines and functionalized ketones in excellent yields with high chemoselectivity. This indicated that triazole ligands are helpful in forming gold nanoparticles and delaying agglomeration in these reactions. Importantly, this kind of air and moisture stable complex was effective for allene synthesis through the 3,3-rearrangement of propargyl ethers with good yields under wet conditions with a reduced catalyst loading by a silver-free protocol. Furthermore, the synthesis of 1,5-enyne derivatives was realized from propargyl alcohols with pyridyltriazole gold(I) complexes as the catalyst.

Violacein is a naturally occurring anticancer therapeutic compound with deep purple color. In this work, we harnessed the modular and combinatorial feature of a Golden Gate assembly method to construct a library of violacein producing strains in the oleaginous yeast Yarrowia lipolytica, where each gene in the violacein pathway was controlled by three different promoters with varying transcriptional strength. After optimizing the linker sequence and the Golden Gate reaction, we achieved high transformation efficiency and obtained a panel of representative Y. lipolytica recombinant strains. By evaluating the gene expression profile of 21 yeast strains, we obtained three colorful compounds in the violacein pathway: green (proviolacein), purple (violacein), and pink (deoxyviolacein). Our results indicated that strong expression of VioB, VioC, and VioD favors violacein production with minimal byproduct deoxyvioalcein in Y. lipolytica, and high deoxyviolacein production was found strongly associated with the weak expression of VioD. By further optimizing the carbon to nitrogen ratio and cultivation pH, the maximum violacein reached 70.04 mg/L with 5.28 mg/L of deoxyviolacein in shake flasks. Taken together, the development of Golden Gate cloning protocols to build combinatorial pathway libraries, and the optimization of culture conditions set a new stage for accessing the violacein pathway intermediates and engineering violacein production in Y. lipolytica. This work further expands the toolbox to engineering Y. lipolytica as an industrially relevant host for plant or marine natural product biosynthesis.