A series of Pd−WO x /Al 2 O 3 catalysts with different contents of WO x were prepared by stepwise incipient wetness impregnations. The influence of WO x on the physicochemical properties of Pd−WO x /Al 2 O 3 catalysts, as well as their catalytic performance for the hydrogenolysis of glucose to 1,2-propanediol (1,2-PDO), was investigated. At low surface W density (0.3−2.1 W nm −2 ), distorted isolated WO x and oligomeric WO x are present on the Pd−WO x /Al 2 O 3 catalysts. Furthermore, isolated WO 4 are the dominating species on the Pd−WO x (5%)/Al 2 O 3 catalyst. When the W density increased to 3.1 W nm −2 , polymeric WO x species are dominant on the Pd−WO x (30%)/Al 2 O 3 catalyst. The Pd surface area decreased while the acid amount increased with increasing W density. Furthermore, increased Lewis acid sites are provided by isolated WO 4 and oligomeric WO x species whereas increased Brønsted acid sites exist on polymeric WO x species. Lewis acid sites promote glucose isomerization to fructose, which is an intermediate in glucose hydrogenolysis to 1,2-PDO. Metal sites catalyze CO hydrogenation and C−C hydrogenolysis, which avoid the coke formation on catalysts. 1,2-PDO selectivity is dependent on the synergy of Lewis acid and metal sites; however, Brønsted acid sites have no contribution to the 1,2-PDO production. Typically, the Pd−WO x (5%)/Al 2 O 3 catalyst possessing the optimal balance of Lewis acid and the metal site shows a 1,2-PDO selectivity of 60.8% at a glucose conversion of 92.2% and has a lifetime of over 200 h.

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The tyrosine metabolism pathway serves as a starting point for the production of a variety of structurally diverse natural compounds in plants, such as tocopherols, plastoquinone, ubiquinone, betalains, salidroside, benzylisoquinoline alkaloids, and so on. Among these, tyrosine-derived metabolites, tocopherols, plastoquinone, and ubiquinone are essential to plant survival. In addition, this pathway provides us essential micronutrients (e.g., vitamin E and ubiquinone) and medicine (e.g., morphine, salidroside, and salvianolic acid B). However, our knowledge of the plant tyrosine metabolism pathway remains rudimentary, and genes encoding the pathway enzymes have not been fully defined. In this review, we summarize and discuss recent advances in the tyrosine metabolism pathway, key enzymes, and important tyrosine-derived metabolites in plants.

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Tanshinone IIA (TIIA), a diterpene quinone with a furan ring, is a bioactive compound found in the medicinal herb redroot sage (Salvia miltiorrhiza Bunge), in which both furan and dihydrofuran analogs are present in abundance. Progress has been made recently in elucidating the tanshinone biosynthetic pathway, including heterocyclization of the dihydrofuran D-ring by cytochrome P450s (CYPs); however, dehydrogenation of dihydrofuran to furan, a key step of furan ring formation, remains uncharacterized. Here, by differential transcriptome mining, we identified six 2-oxoglutarate-dependent dioxygenase (2-ODD) genes whose expressions corresponded to tanshinone biosynthesis. We showed that Sm2-ODD14 acts as a dehydrogenase catalyzing the furan ring aromatization. In vitro Sm2-ODD14 converted cryptotanshinone (CT) to TIIA and thus was designated TIIA synthase (SmTIIAS). Further, SmTIIAS showed a strict substrate specificity, and repression of SmTIIAS expression in hairy root by RNAi led to increased accumulation of total dihydrofuran-tanshinones and decreased production of furan-tanshinones. We conclude that SmTIIAS controls the metabolite flux from dihydrofuran- to furan-tanshinones, which influences medicinal properties of S. miltiorrhiza.