Search results for " Synthesis"
showing 10 items of 1625 documents
Radiosynthesis of 1-(4-(2-[18F]fluoroethoxy)benzenesulfonyl)-3-butyl urea: a potentialβ-cell imaging agent
2002
Summary Tolbutamide (1) is a sulfonurea agent used to stimulate insulin secretion in type 2 diabetic patients. Its analogue 1-(4-(2-[ 18 F]fluoroethoxy)benzenesulfonyl)-3butyl urea (3) was synthesized in overall radiochemical yields of 45% as a potential b-cell imaging agent. Compound 3 was synthesized by 18 F-fluoroalkylation of the corresponding hydroxy precursor (2 )w ith 2-[ 18 F]fluoroethyltosylate in DMF at 1208C for 10 min followed by purification with HPLC in a synthesis time of 50 min. Insulin secretion experiments of the authentic 19 F-standard compound on rat islets showed that the compound has a similar stimulating effect on insulin secretion as that of tolbutamide (1). The part…
Synthesis of 1-Palmitoyl-2-((E)-9- and (E)-10-nitrooleoyl)-sn-glycero-3-phosphatidylcholines
2019
Extensive investigation of nitrated phospholipids in connection with various biologically important processes requires reliable access to suitable material. A selective chemical synthesis introducing a defined nitrofatty acid at the sn-2 position of a 2-lyso sn-glycero-3-phosphatidylcholine was developed. Given that the nitroalkene moiety of both reactant nitrofatty acid derivative and the product esters is characterised by particular sensitivity to nucleophile addition and, depending on the intermediate, subsequent olefin isomerisation and retro-Henry-type reaction, a reliable two-step ester formation was introduced. The activation of the nitrofatty acid succeeded after reaction with trich…
Second-Line Endocrine Treatment
1988
It was a milestone of cancer therapy in general when Huggins et al. [1] in 1941 first reported the beneficial clinical effects of bilateral orchiectomy in patients with prostate cancer, and the use of castration or estrogens as standard therapy remained the first- line treatment for many years. It was furthermore the beginning of a development which, over the following decades, led to the manipulation of testicular androgen synthesis and to attempts to eliminate other possible sources of male hormones.
Conservation of optical purity of amino acids: a principal problem in biochemical and proto-biochemical systems.
1981
Dor L-amino acids, regardless of their state (peptide-bound or free, in the solid state or in aqueous solution), tend to racemize. In a living cell this racemization is usually compensated by specific degradation and replacement of the unwanted polypeptides that contain the wrong enantiomers. But a few long-lived proteins that are synthesized at or near birth are never replaced. Well investigated is the racemization of L-aspartic acid at a rate of 0.1 to 1.14 per cent per year in proteins from lenses and dentine. Increased racemization of eye lens proteins has been related to a form of human eye disease known as brunescent cataracts. Also quite well investigated is the racemization of amino…
On the Theoretical Limits of Noise-Gain-Mismatch Tradeoff in the Design of Multi-Stage Cascaded Transistor Amplifiers
2007
The problem of evaluating the limit performances of cascaded single-ended multi-stage transistor amplifiers is addressed. In particular, a theoretically rigorous approach is proposed for the determination of a family of optimal design curves (ODC's) which express the best (maximum optimal) noise-gain tradeoff that can be achieved - at each operating frequency - when a simultaneous constraint on amplifier input VSWR is accounted for.
Clinical value of diascopy and other non-invasive techniques on differential diagnosis algorithms of oral pigmentations: a systematic review
2016
Objectives To determine the diagnostic value of diascopy and other non-invasive clinical aids on recent differential diagnosis algorithms of oral mucosal pigmentations affecting subjects of any age. Material and Methods Data Sources: this systematic review was conducted by searching PubMed, Scopus, Dentistry & Oral Sciences Source and the Cochrane Library (2000-2015); Study Selection: two reviewers independently selected all types of English articles describing differential diagnosis algorithms of oral pigmentations and checked the references of finally included papers; Data Extraction: one reviewer performed the data extraction and quality assessment based on previously defined fields whil…
Chiral bis(amino alcohol)oxalamides as ligands for asymmetric catalysis. Ti(IV) catalyzed enantioselective addition of diethylzinc to aldehydes
2005
Abstract Several chiral bis(aminoalcohol)oxalamides with C 2 -symmetry have been prepared and used as ligands for the enantioselective addition of diethylzinc to aromatic and aliphatic aldehydes. The reaction proceeds in the presence of titanium isopropoxide to give the corresponding ( S )-alcohols with ee up to 78%. In the absence of Ti(IV), the alcohols with the opposite configuration are obtained.
Synthesis of 2-isoxazolines: enantioselective and racemic methods based on conjugate additions of oximes.
2010
The formation of 3-unsubstituted 2-isoxazolines by means of condensation reactions between α,β-unsaturated aldehydes and oximes proceeds readily in the presence of catalytic amounts of anilinium salts. Mechanistically, the process involves a fast conjugate addition of the oxime and a slower intramolecular oxime-transfer reaction. The rate of oxime transfer was found to correlate with the acidity of the catalyst. This finding enabled us to discover an enantioselective process in which the fragile conjugate-addition product generated in the first stage is rapidly cyclized into the stable isoxazoline under acidic conditions, with conservation of enantiomeric excess. In summary, herein we descr…
Enantioselective zinc-mediated conjugate addition of terminal alkynes to enones.
2012
Zinc for conjugate alkynylation: The enantioselective conjugate addition of terminal alkynes to 2-arylidene-1,3-diketones in the presence of diethylzinc and a catalytic amount of (R)-VANOL has been developed. The reaction can be applied to different aromatic and heteroaromatic alkynes and enones, giving the expected products in good yield and with enantiomeric excesses up to 91%. The products can be enantiomerically enriched up to 99% ee by crystallization (see scheme).
Highly selective electrosynthesis of biphenols on graphite electrodes in fluorinated media.
2011
The direct and selective phenol coupling reaction that provides biphenols still represents a challenge in organic synthesis. The recently developed electrosynthesis on boron-doped diamond anodes with fluorinated additives was developed further to allow the application to less-expensive electrodes and fluorinated media. This advanced protocol allows the highly selective anodic phenol coupling reaction on graphite with a broad scope.