Chemoenzymatic Synthesis of the Cyclopiane Family of Diterpenoid Natural Products.

A three-stage chemoenzymatic synthesis of the cyclopiane family and related diterpenes is reported. Deoxyconidiogenol with a 6/5/5/5-fused tetracyclic cyclopiane skeleton was first produced by an engineered E. coli host harboring the corresponding terpene cyclase PchDS.

Topological corner states in a silicon nitride photonic crystal membrane with a large bandgap.

The theory of band topology has inspired the discovery of various topologically protected states in the regime of photonics. It has led to the development of topological photonic devices with robust property and versatile functionalities, like unidirectional waveguides, compact power splitters, high-Q resonators, and robust lasers. These devices mainly rely on the on-chip photonic crystal (PhC) in Si or III-V compound materials with a fairly large bandgap.

Phase-preserving NALM regenerator with lower input power by optimizing the nonreciprocal phase shifter.

We propose a new nonlinear amplifying loop mirror (NALM)-based phase-preserving amplitude regenerator (so-called NP-NALM) by introducing a nonreciprocal phase shifter to further improve the regeneration performance. The theoretical model of the NP-NALM structure and the amplitude regeneration and phase-preserving conditions are presented. It is shown that the optimal working point power reduces with the increase of the nonreciprocal phase shift in the available range and the first working point power can be as low as 115 mW by optimizing the nonreciprocal phase shifter.

Characterization of Enzymes Catalyzing the Formation of the Nonproteinogenic Amino Acid l-Dap in Capreomycin Biosynthesis.

Capreomycin (CMN) and viomycin (VIO) are nonribosomal peptide antituberculosis antibiotics, the structures of which contain four nonproteinogenic amino acids, including l-2,3-diaminopropionic acid (l-Dap), β-ureidodehydroalanine, l-capreomycidine, and β-lysine. Previous bioinformatics analysis suggested that CmnB/VioB and CmnK/VioK participate in the formation of l-Dap; however, the real substrates of these enzymes are yet to be confirmed. We herein show that starting from -phospho-l-Ser (OPS) and l-Glu precursors, CmnB catalyzes the condensation reaction to generate a metabolite intermediate -(1-amino-1-carboxyl-2-ethyl)glutamic acid (ACEGA), which undergoes NAD-dependent oxidative hydrolysis by CmnK to generate l-Dap.