Total Synthesis of (+)-Cyclobutastellettolide B.

A convenient enantioselective total synthesis of (+)-cyclobutastellettolide B via a strategy that involves a diastereoselective Johnson-Claisen rearrangement, a regioselective cyclopropoxytrimethylsilane ring-opening reaction, and a Norrish-Yang cyclization is described. The results of computational and experimental studies indicate that the regio- and stereoselectivity of the Norrish-Yang reaction are controlled by the C-H bond dissociation energy and restricted rotation of the C13-C14 bond.

Asymmetric Total Synthesis of (-)-Spirochensilide A, Part 2: The Final Phase and Completion.

The final phase of the total synthesis of (-)-spirochensilide A is described. A tungsten-mediated cyclopropene-based Pauson-Khand reaction was developed to form the spiral CD ring system with desired stereochemistry at the C13 quaternary center. Other important steps enabling completion of this synthesis included an intermolecular aldol condensation to link the ABCD core with the EF fragment and a Cu-mediated 1,4-addition to stereoselectively install the C21 stereogenic center. The chemistry developed for this total synthesis of (-)-spirochensilide A (1) will aid the synthesis of polycyclic natural products bearing this unique spiral ring system.

Asymmetric Total Synthesis of (-)-Spirochensilide A, Part 1: Diastereoselective Synthesis of the ABCD Ring and Stereoselective Total Synthesis of 13(R)-Demethyl Spirochensilide A.

A concise and diastereoselective construction of the ABCD ring system of spirochensilide A is described. The key steps of this synthesis are a semipinacol rearrangement reaction to stereoselectively construct the AB ring system bearing two vicinal quaternary chiral centers and a Co-mediated Pauson-Khand reaction to form the spiro-based bicyclic CD ring system. This chemistry leads to the stereoselective synthesis of 13(R)-demethyl spirochensilide A, paving the way for the first asymmetric total synthesis of (-)-spirochensilide A.

Asymmetric Total Synthesis of (-)-Spirochensilide A.

An asymmetric total synthesis of (-)-spirochensilide A has been achieved for the first time. The synthesis features a semipinacol rearrangement reaction to stereoselectively construct the two-vicinal quaternary chiral centers at C8 and C10, a tungsten-mediated cyclopropene-based Pauson-Khand reaction to install the C13 quaternary chiral center, and a furan-based oxidative cyclization to stereoselectively form the spiroketal motif.

Asymmetric Total Synthesis of Propindilactone G.

A concise total synthesis of (+)-propindilactone G, a nortriterpenoid isolated from the stems of Schisandra propinqua var. propinqua, has been achieved for the first time. The key steps of the synthesis include an asymmetric Diels-Alder reaction, a Pauson-Khand reaction, a Pd-catalyzed reductive hydrogenolysis reaction, and an oxidative heterocoupling reaction. These reactions enabled the synthesis of (+)-propindilactone G in only 20 steps. As a consequence of our synthetic studies, the structure of (+)-propindilactone G has been revised.

Oil Bodies Extracted from High-Fat and Low-Fat Soybeans: Stability and Composition During Storage.

Soybeans contain oil bodies (OBs) that encapsulate triacylglycerols (TAGs) with a phospholipid monolayer carrying scattered proteins. In nature, soybean OBs can form natural emulsions in aqueous media and may serve as natural, minimally processed, stable, and pre-emulsified oil for addition into appropriate food systems. In this study, OBs were obtained by aqueous extraction from the mature seeds of 2 soybean crop cultivars, high-fat soybean and low-fat soybeans. The compositions of the extracted OBs were analyzed during storage at room temperature up to 14 d (pH = 7). The oxidative stability of these OBs, stored at 60 °C, was evaluated by measuring the presence of primary (lipid hydroperoxides) and secondary lipid oxidation products (malondialdehyde) by determining the standard peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) value. During storage, the contents of unsaturated fatty acids, phospholipids, and tocopherols declined in both OBs, while their mean particle diameters (d32 ) and ζ-potentials increased. The changes in PV and TBARS values exhibited a similar trend for both OBs, but the OBs from low-fat soybeans had significantly lower PV and higher TBARS values than the OBs from high-fat soybean cultivars (P < 0.05). Overall, the OBs from both soybean cultivars had good stability during storage.

Asymmetric Total Synthesis of Propindilactone†G, Part†3: The Final Phase and Completion of the Synthesis.

Two independent synthetic approaches were evaluated for the final phase of the asymmetric total synthesis of propindilactone G (1). The key steps that led to the completion of the asymmetric total synthesis included: 1) an intermolecular oxidative heterocoupling reaction of enolsilanes to link the core structure to the side chain; 2) an intermolecular Wittig reaction for the formation of the α,ß,γ,δ-unsaturated ester; and 3) a regio- and stereoselective OsO4 -catalyzed dihydroxylation of an α,ß,γ,δ-unsaturated enone, followed by an intramolecular lactonization reaction to afford the final product. These reactions enabled the synthesis of (+)-propindilactone G in only 20 steps. As a consequence of our synthetic studies, the structure of (+)-propindilactone G has been revised. Furthermore, the direct oxidative coupling strategy for ligation of the core of propindilactone G with its side chain may find application in the syntheses of other natural products and complex molecules.

Asymmetric Total Synthesis of Propindilactone†G, Part†2: Enantioselective Construction of the Fully Functionalized BCDE Ring System.

The enantioselective synthesis of the fully functionalized BCDE tetracyclic ring system of propindilactone G (A) is reported. Several synthetic methods were developed and applied to achieve this goal, including: 1) an asymmetric Diels-Alder reaction in the presence of Hayashi's catalyst for the synthesis of optically pure key intermediate 3; 2) an intramolecular Pauson-Khand reaction (PKR) for the stereoselective synthesis of the BCDE ring with an all-carbon chiral quaternary center at the C13 position by using the TMS-substituted acetylene as the substrate; and 3) Pd-catalyzed reductive hydrogenolysis for the stereoselective synthesis of the fully functionalized BCDE tetracyclic ring system. The chemistry developed herein provided a greater understanding of the total synthesis propindilactone G (A) and its analogues.