Synthetic Studies on Enantioselective Total Synthesis of Cyathane Diterpenoids: Cyrneines A and B, Glaucopine C, and (+)-Allocyathin B2.

The details for the synthetic studies on enantioselective total synthesis of cyathane diterpenoids cyrneine A (1) and B (2), glaucopine C (3), and (+)-allocyathin B2 are presented. We established a mild Suzuki coupling for heavily substituted nonactivated cyclopentenyl triflates using a phosphinamide-derived palladacycle as precatalyst and a chelation-controlled highly regioselective Friedel-Crafts cyclization. The utilization of these two key reactions enabled a rapid construction of the 5-6-6 tricyclic skeleton. In the middle stage of the synthesis, a Birch reductive methylation, a modified Wolff-Kishner-Huang reduction, and a carbenoid-mediated ring expansion were employed as the key reactions to furnish the 5-6-7 tricyclic core bearing two antiorientated all-carbon quaternary stereocenters at the C6 and C9 ring junctions. By applying these key transformations, a more efficient total synthesis of cyrneine A and allocyathin B2, and the first total synthesis of cyrneine B and glaucopine C, were accomplished through a collective manner. The late-stage conversions involving a base-mediated double bond migration and a double bond migration/aerobic γ-CH oxidation cascade for the stereoselective synthesis of cyrneine B and glaucopine C were interesting.

A Total Synthesis of (-)-Hamigeran B and (-)-4-Bromohamigeran B.

A concise synthesis of (-)-hamigeran B and (-)-4-bromohamigeran B is presented. The key reactions include a Suzuki coupling of enol triflate 15 with arylboronic ester for efficient synthesis of the densely 1,2,3-trisubstituted cyclopentene 23, a coordination-controlled intramolecular Friedel-Crafts cyclization of free phenol 13 for highly regioselective construction of tricyclic core 12, and a LiOH/O2-promoted hydrolysis and concomitant aerobic oxidation of 31 for atom- and step-economic accessing of diketone 32. The application of these key transformations allowed for a rapid and efficient synthesis of (-)-hamigeran B and (-)-4-bromohamigeran B in 13 steps from the readily available chiral material 18.

[Physiological response of the distribution of non-structural carbohydrates to water stress in wheat].

In this paper, the spring wheat (cv. Xihan No. 2) was taken as research material to investigate the dynamic changes of the non-structural carbohydrates (NSC) in flag leaves, stems and leaf sheaths and activities of carbon-metabolizing enzymes (SSS, GBSS) in grains during wheat development process under various water stresses by water stress and re-watering treatment methods. The results indicated that various water stresses had no significant effects on the sucrose contents in flag leaves, stems, leaf sheaths and other organs of wheat. With the increase of water stress, the content of starch in flag leaves was significantly increased within 12-18 d after flowering. Water stress shortened the starch accumulation period in stems and sheaths after flowering and inhibited the transformation and distribution of starch in wheat stems. The accumulation of starch in sheath also gradually increased, which was early terminated under moderate water stress. At the beginning of the water stress, the contents of NSC in vegetative organs were listed as: flag leaves > stems > leaf sheaths. With the increase of water stresses, the NSC contents in vegetative organs were listed as: stems > flag leaves > leaf sheaths. We could conclude that the changes in main NSC (sugar, starch) distribution and carbon-metabolism enzyme activities was a kind of physiological regulation response of wheat to water stresses.