Anomalous 1 H NMR chemical shift behavior of substituted benzoic acid esters.

Benzoic acid esters represent key building blocks for many drug discovery and development programs and have been advanced as potent PDE4 inhibitors for inhaled administration for treatment of respiratory diseases. This class of compounds has also been employed in myriad industrial processes and as common food preservatives. Recent work directed toward the synthesis of intermediates for a proprietary medicinal chemistry program led us to observe that the 1 H NMR chemical shifts of substituents ortho to the benzoic acid ester moiety defied conventional iterative chemical shift prediction protocols. To explore these unexpected results, we initiated a detailed computational study employing density functional theory (DFT) calculations to better understand the unexpectedly large variance in expected versus experimental NMR chemical shifts.

Contrasting Diastereoselectivity between Cyclic Nitrones and Azomethine Ylides. Stereocontrolled Pathways to cis-anti-anti-cis-Oxazatetraquinanes from a Bicyclic Nitrone.

A study of [3 + 2] cycloaddition reactions of a bicyclic nitrone with various cyclopentenes has clarified the diastereomeric preferences as a function of the olefinic structure. It has also identified an important stereochemical difference between nitrones and the analogous azomethine ylides in [3 + 2] cycloaddition reactions.

BF3·OEt2-Catalyzed Unexpected Stereoselective Formation of 2,4-trans-Diallyl-2-methyl-6-aryltetrahydro-2H-pyrans with Quaternary Stereocenters.

The present manuscript describes a convenient, mild, and highly stereoselective method for the allylation of δ-hydroxy-α,ß-unsaturated ketones having a benzylic hydroxyl group at the δ-position using allyltrimethylsilane mediated by BF3·OEt2, leading to 2,4-diallyl-2-methyl-6-aryltetrahydro-2H-pyran ring systems with quaternary carbon stereogenic centers. This represents the first example of a tandem isomerization followed by one C-O and two C-C bond-forming reactions in one pot. The isolation of TMS-protected lactol as an intermediate from the reaction strongly supports the proposed mechanistic pathway.

Unraveling the C2-Symmetric Azatetraquinane System. Simple, Enantioselective Syntheses.

Concise stereocontrolled synthetic routes to the C2-symmetric azatetraquinane 1 (or, also, the enantiomer) are described. The successful execution of the synthesis involved innovation in the methodology for [3+2] cycloaddition and stereochemical control.

Enantioselective Conversion of Oligoprenol Derivatives to Macrocycles in the Germacrene, Cembrene, and 18-Membered Cyclic Sesterterpene Series.

A new enantio-and diastereoselective process has been developed for the efficient conversion of farnesol and other oligoprenyl alcohols to chiral 10-, 14-, and 18-membered cyclization products, including germacrenol, (+)-costunolide, 3-ß-elemol, and epi-mukulol. The key cyclization reaction utilizes ω-bromo aldehyde substrates, a chiral ligand, and indium powder as the reagent at -78 °C and generates 10-, 14-, and 18-membered cyclic products in 70-74% yield and 94-95% ee.

A General Diastereoselective Strategy for Both cis- and trans-2,6-Disubstituted Tetrahydropyrans: Formal Total Synthesis of (+)-Muconin.

A protocol for general diastereoselective tandem dihydroxylation followed by SN2 cyclization was developed for the convenient and efficient synthesis of cis- and trans-2,6-disubstituted tetrahydropyrans from ζ-mesyloxy α,ß-unsaturated esters. The application of this novel method was demonstrated through the concise formal synthesis of (+)-muconin, a nonclassical acetogenin, with sequential THP-THF ring formation.

Highly stereocontrolled synthesis of trans-2,6-disubstituted-5-methyl-3,6-dihydropyrans: stereoselective synthesis of the bicyclic core of penostatin B.

An efficient, mild, and highly diastereoselective strategy for the synthesis of trans-2,6-disubstituted-5-methyl-3,6-dihydropyran ring systems has been developed starting from δ-hydroxy α-methyl α,ß-unsaturated aldehydes and allyltrimethylsilane in the presence of a catalytic amount of ZnBr2 in a highly diastereoselective manner with excellent yield. The versatility of the above method was also demonstrated for the construction of the bicyclic core present in penostatin B in a concise and highly stereoselective manner.

Stress-inducible expression of At DREB1A in transgenic peanut (Arachis hypogaea L.) increases transpiration efficiency under water-limiting conditions.

Water deficit is the major abiotic constraint affecting crop productivity in peanut (Arachis hypogaea L.). Water use efficiency under drought conditions is thought to be one of the most promising traits to improve and stabilize crop yields under intermittent water deficit. A transcription factor DREB1A from Arabidopsis thaliana, driven by the stress inducible promoter from the rd29A gene, was introduced in a drought-sensitive peanut cultivar JL 24 through Agrobacterium tumefaciens-mediated gene transfer. The stress inducible expression of DREB1A in these transgenic plants did not result in growth retardation or visible phenotypic alterations. T3 progeny of fourteen transgenic events were exposed to progressive soil drying in pot culture. The soil moisture threshold where their transpiration rate begins to decline relative to control well-watered (WW) plants and the number of days needed to deplete the soil water was used to rank the genotypes using the average linkage cluster analysis. Five diverse events were selected from the different clusters and further tested. All the selected transgenic events were able to maintain a transpiration rate equivalent to the WW control in soils dry enough to reduce transpiration rate in wild type JL 24. All transgenic events except one achieved higher transpiration efficiency (TE) under WW conditions and this appeared to be explained by a lower stomatal conductance. Under water limiting conditions, one of the selected transgenic events showed 40% higher TE than the untransformed control.