429 research outputs found
Modification of chiral dimethyl tartrate through transesterification : immobilisation on POSS and enantioselectivity reversion in Sharpless asymmetric epoxidation
No full textModification of dimethyl tartrate has been investigated through transesterification with aminoalcohols to provide reactive functionalities for the covalent bonding of chiral tartrate to polyhedral oligomeric silsesquioxanes. The transesterification of dimethyl tartrate has been widely studied by means of using different catalytic systems and reaction conditions. Through the proper selection of both, the catalytic system and the reaction conditions, it is possible to achieve the mono- or the bis-substituted tartrate derivative as sole products. All the intermediate chiral tartrate-derived ligands were successfully used in the homogeneous enantioselective epoxidation of allylic alcohols providing moderate enantiomeric excess over the products. Attached amine groups have been used to support the modified tartrate ligands onto a haloaryl-functionalized silsesquioxane moiety. This final chiral tartrate ligand displays enantioselectivity reversion in the asymmetric epoxidation of allylic alcohols with regards to the starting dimethyl tartrate ligand, having both molecules them the same chiral sign. However, the POSS-containing ligand can be easily recovered in almost quantitative yield and reused in asymmetric epoxidation reactions. In addition, recovered silsesquioxane-pendant ligand, though displaying decreasing catalytic activity in recycling epoxidation tests, showed very stable enantioselective behavior
sj-docx-1-whe-10.1177_17455065211070548 – Supplemental material for Enhancing domestic violence advocates’ ability to discuss HIV pre-exposure prophylaxis (PrEP): Feasibility and acceptability of an educational intervention
No full textSupplemental material, sj-docx-1-whe-10.1177_17455065211070548 for Enhancing domestic violence advocates’ ability to discuss HIV pre-exposure prophylaxis (PrEP): Feasibility and acceptability of an educational intervention by Tiara C Willie, Laurel Sharpless, Mauda Monger, Trace S Kershaw, Wendy B Mahoney and Jamila K Stockman in Women’s Health</p
First concise total synthesis of 5-epi-prelactone B
No full textFirst short total synthesis of 5-epi-prelactone B has been achieved involving Sharpless asymmetric epoxidation and intramolecular hydride transfer reaction for formation of the aldol product by nonaldol chemistry as the key steps
Multigramme synthesis and asymmetric dihydroxylation of a 4-fluorobut-2E-enoate
No full textEsters of crotonic acid were brominated on a multigramme scale using a free radical procedure. A phase transfer catalysed fluorination transformed these species to the 4-fluorobut-2E-enoates reproducibly and at scale (48–53%, ca. 300 mmol). Asymmetric dihydroxylation reactions were then used to transform the butenoate, ultimately into all four diastereoisomers of a versatile fluorinated C4 building block at high enantiomeric-enrichment. The (DHQ)2AQN and (DHQD)2AQN ligands described by Sharpless were the most effective. The development and optimisation of a new and facile method for the determination of ee is also described; 19F{1H} spectra recorded in d-chloroform/diisopropyl tartrate showed distinct baseline separated signals for different enantiomers
Synthetic sequence specific DNA binding molecules
No full textThe design of sequence specific DNA-binding molecules has advanced in recent years due, in part, to the development of analytical techniques such as footprinting and affinity cleaving which allow rapid and precise analysis of hundreds of of potential DNA binding sites. The construction of synthetic molecules that bind in the minor and major groove of DNA with incrementally increasing sequence specificity is simply the first step toward developing a set of rules for the three-dimensional readout of double helical DNA
Synthetic studies toward potent cytotoxic agent amphidinolide B: synthesis of the entire Cl-C13 moiety of the bottom half
No full textSharpless asymmetric dihydroxylation and Nozaki-Hiyama-Kishi's Cr(II)-mediated coupling between an α-alkoxyaldehyde and a vinyl iodide are the key steps in the stereoselective synthesis of the entire C1-C13 segment of the bottom-half of amphidinolide B
Total Syntheses of All Stereoisomers of Phenatic Acid B
No full textThe total syntheses of all stereoisomers of phenatic acid B and determination of their absolute configuration are described. The synthetic strategy is based on an efficient combination of the Sharpless asymmetric dihydroxylation, the Johnson−Claisen rearrangement, and hydroboration−oxidation. It involves 11−12 steps and overall yield of 5−8%
Total Syntheses of All Stereoisomers of Phenatic Acid B
No full textThe total syntheses of all stereoisomers of phenatic acid B and determination of their absolute configuration are described. The synthetic strategy is based on an efficient combination of the Sharpless asymmetric dihydroxylation, the Johnson−Claisen rearrangement, and hydroboration−oxidation. It involves 11−12 steps and overall yield of 5−8%
Total Syntheses of All Stereoisomers of Phenatic Acid B
No full textThe total syntheses of all stereoisomers of phenatic acid B and determination of their absolute configuration are described. The synthetic strategy is based on an efficient combination of the Sharpless asymmetric dihydroxylation, the Johnson−Claisen rearrangement, and hydroboration−oxidation. It involves 11−12 steps and overall yield of 5−8%
Stereoselective Synthesis of the C1–C16 Fragment of the Purported Structure of Formosalide B
No full textThe first stereoselective synthesis of the C1-C16 fragment possessing stereo-enriched fully substituted tetrahydropyran (THP) along with tetrahydrofuran (THF) rings of the proposed structure of formosalide B is described in 12 longest linear steps with 22% overall yield, starting from two cheap and commercially available 1,5-pentanediol and l-glutamic acid, following a convergent approach. The key steps involve in this synthesis are Horner-Wadsworth-Emmons reaction, Sharpless asymmetric dihydroxylation, and acid-mediated ketalization to assemble the substituted THP ring, one-pot Sharpless dihydroxylation-SN2-type cyclization, and Wittig homologation to construct the THF derivative
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