Search results for "Chemical Synthesis"
showing 10 items of 285 documents
Mandelamide-zinc-catalyzed enantioselective alkyne addition to heteroaromatic aldehydes.
2006
The (S,S)-mandelamide III catalyzes the additions of both aryl- and alkylalkynylzinc reagents to heteroaromatic aldehydes with good yields and enantioselectivities up to 92%. This catalyst is easily prepared in a one-step procedure, and both enantiomers are available. Unlike most other described methods, using this catalyst does not require the addition of Ti(O(i)Pr)4.
Synthesis and Photoluminescent Properties of 1,1‘-Binaphthyl-Based Chiral Phenylenevinylene Dendrimers
2003
New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6â²-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1â²-binaphthyl derivative (R)-1 and the appropriate dendrons (R)2nGn-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, t…
Syntheses of novelN-([18F]fluoroalkyl)-N-nitroso-4-methyl-benzenesulfonamides and decomposition studies of corresponding19F- and bromo-analogues: pot…
2003
N-([ 18 F]fluoroalkyl)-N-nitroso-4-methyl-benzensulfonamides [n-alkyl = (-CH 2 ) [ 18,19 F]F, n=2-4)] were synthesized in radiochemical yields ranging from 75-90% to provide new secondary labelling precursors for the syntheses of 18 F-labelled compounds. Preliminary decomposition studies utilizing the corresponding non-radioactive 19 F-compounds as well as the bromo containing analogous compounds were performed to evaluate their stability regarding temperature and basicity of the labelling medium. Furthermore, initial difficulties in labelling these compounds led to the development of a modified labelling procedure applying nearly solvent-free conditions. Extensive decomposition experiments…
Radiosynthesis of (±)-(2-((4-(2-[18F]fluoro-ethoxy)phenyl)bis(4-methoxy-phenyl)methoxy)ethylpiperidine-3-carboxylic acid: a potential GAT-3 PET ligan…
2001
A dysfunction of GABAergic neurotransmission is related to diseases such as epilepsy, Huntington-disease and Parkinson-syndrome. A new 18F-fluorine labelled GABA transporter ligand for the GABA-transporter subtype GAT-3 was developed which may allow the in vivo visualisation of GABAergic neurotransmission. The precursors ethyl (2-(4-hydroxyphenyl)bis(4-methoxyphenyl)-methoxy)ethyl)-piperidine-3-carboxylate and ethyl(2-((4-(2-tosylethoxy)phenyl)-bis(4-methoxyphenyl)-methoxy) ethyl)-piperidine3-carboxylate were synthesised and labelled by the use of 2-[18F]fluoroethyltosylate or [18F]fluoride. Subsequent cleavage of the ester moiety gave the final product (±)-(2-((4-(2-[18F]fluoroethoxy)pheny…
Chemoenzymatic-Chemical Synthesis of a (2-3)-Sialyl T Threonine Building Block and Its Application to the Synthesis of the N-Terminal Sequence of Leu…
2001
Protection of all functional groups of the carbohydrate portion of the chemoenzymatically synthesized sialyl T threonine ester 1 (R=R1 =H, R2 =tBu, Fmoc=9-fluorenylmethoxycarbonyl) and subsequent acidolysis of the tert-butyl ester afforded the building block 2 (R=Ac, R1 =Me, R2 =H). The latter is a useful tool in the solid-phase synthesis of the N-terminal sequence 3 of the leukemia-associated leukosialin.
Large Scale Synthesis of Mono- and Di-urethane Derivatives of Lysine.
1999
Orthogonally protected diurethane derivatives of lysine are valuable materials for peptide syntheses. An example is ZLys(Boc), which is exploited in the industrial production of certain well-established peptide drugs. 3,4) Another derivative is Fmoc-Lys(Boc), which is in common use in the laboratory synthesis of peptides. 5) The simplest route to these lysine derivatives seems to be using the copper complex for simultaneous protection of the a-amino and a-carboxyl function, N e -tert-butoxycarbonylation and then copper detachment. The obtained Lys(Boc) might be then subjected to N a -benzyloxycarbonylation.
Straightforward Stereoselective Access to Cyclic Peptidomimetics
2009
The preparation of cyclic dipeptide mimetics from chiral imino lactones derived from (R)-phenylglycinol is described. Key steps of the synthetic route included the fully stereoselective construction of a quaternary center, the formation of six-, seven-, or eight-membered lactams by means of an RCM cyclization, and the introduction of a new amino group within the lactam ring. The synthesis of a tripeptide mimetic is also reported.
Enzymatic glycosylation of o-glycopeptides
1992
Abstract O-Glycosylation of serine derivatives carried out with N-urethane protected glucosamine yields O-glycopeptides which are regio- and stereoselectively galactosylated with the aid of β-1,4-galactosyltransferase (EC 2.4.1.22).
Synthesis of brominated tetrathiafulvalenes via phosphite-mediated cross-coupling
2010
The synthesis of polybrominated tetrathiafulvalenes (TTF-Brn, 2-4) containing 2-4 bromine atoms via phosphite-mediated cross-coupling of bromo-substituted 1,3-dithiole-2-thiones and 1,3-dithiole-2-ones is reported. © 2010 Elsevier B.V.
Highly Diastereoselective Arylation of (S)-Mandelic Acid Enolate: Enantioselective Synthesis of Substituted (R)-3-Hydroxy-3-phenyloxindoles and (R)-B…
2005
An easy access to substituted (R)-3-hydroxy-3-phenyloxindoles, (R)-benzylic acids, and benzophenones is described. The reaction of the lithium enolate of the (2S,5S)-cis-1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with several o- and p-halonitrobenzenes proceeds readily to give the corresponding arylation products in good yields and diastereoselectivities. The reduction of the nitro group with Zn/HCl/EtOH in the o-nitro arylation products with concomitant intramolecular aminolysis of the dioxolanone moiety leads directly to enantiomerically pure (R)-3-hydroxy-3-phenyloxindoles. On the other hand the basic hydrolysis of the dioxolanone moiety in all t…