The surface of acid-activated attapulgite (ATP) was modified by grafting 3-aminopropyltriethoxysilane (APTES) for the immobilization of heteropolyacid salt Co 4 HP 2 Mo 15 V 3 O 62 (CoHPAs). The samples were characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, specific surface area measurements, thermal analysis and field emission scanning electron microscopy. The catalytic activity was tested for the oxidation of ethylbenzene in the presence of 50 % H 2 O 2 for the first time in this work. It was found that the activity of the ATP supported CoHPAs catalyst is obviously influenced by APTES grafting. The CoHPAs/ATP APTES catalyst exhibits high activity owing to the silylation of ATP, with the conversion of ethylbenzene and selectivity of acetophenone up to 72.7 and 95.4 %, respectively. The results also show that the CoHPAs/ATP APTES catalyst can be reused at least five times without significant decrease of activity.
Didemnins are a class of cyclic depsipeptides derived from sea tunicates that exhibit potent anticancer, antiviral, and immunosuppressive properties. Although certain Tistrella species can produce didemnins, their complete biosynthetic potential remains largely unexplored. In this study, we utilize feature-based molecular networking to analyze the metabolomics of Tistrella mobilis and Tistrella bauzanensis, focusing on the production of didemnin natural products. In addition to didemnin B, we identify nordidemnin B and [hysp2]didemnin B, as well as several minor didemnin analogs. Heterologous expression of the didemnin biosynthetic gene cluster in a Streptomyces host results in the production of only didemnin B and nordidemnin B in limited quantities. Isotope-labeling studies reveal that the substrate promiscuity of the adenylation domains during biosynthesis leads to the accumulation of nordidemnin B and [hysp2]didemnin B. Additionally, precursor-directed biosynthesis is applied to generate eight novel didemnin derivatives by supplementing the culture with structurally related amino acids. Furthermore, we increased the titers of nordidemnin B and [hysp2]didemnin B by supplementing the fermentation medium with l-valine and l-isoleucine, respectively. Finally, both compounds undergo side-chain oxidation to enhance their biological activity, with their anticancer properties found to be as potent as plitidepsin.
危险品化学品经营许可证（带存储）