Tandem protection

Compound (E) was prepared from levoglucosan and, after transformation into its tosylate and the corresponding epoxide, was opened with DMSO anion to give a dimethylated alcohol after desulfurization. The alcohol was then transformed into the corresponding lactol. Reduction of the lactol to the expected triol followed by a tandem protection-oxidation process afforded an aldehyde, which was then coupled with the vinyllithium reagent generated from the corresponding vinyl iodide [190]. The major diastereoisomer was transformed, after a... 

Tandem cyclization/3-substitution can be achieved starting with o-(trifluoro-acetamido)phenylacetylenes. Cyclization and coupling with cycloalkenyl trif-lates can be done with Pd(PPh3)4 as the catalyst[9]. The Pd presumably cycles between the (0) and (II) oxidation levels by oxidative addition with the triflate and the reductive elimination which completes the 3-alkenylation. The N-protecting group is removed by solvolysis under the reaction conditions, 3-Aryl groups can also be introduced using aryl iodides[9]. 

However, interpretation of, or even obtaining, the mass spectrum of a peptide can be difficult, and many techniques have been introduced to overcome such difficulties. These techniques include modifying the side chains in the peptide and protecting the N- and C-terminals by special groups. Despite many advances made by these approaches, it is not always easy to read the sequence from the mass spectrum because some amide bond cleavages are less easy than others and give little information. To overcome this problem, tandem mass spectrometry has been applied to this dry approach to peptide sequencing with considerable success. Further, electrospray ionization has been used to determine the molecular masses of proteins and peptides with unprecedented accuracy. 

A 11011-addition procedure based on a tandem retroaldol/epoxide-opening/cycli-zation sequence has been utilized for the elaboration of the dihydrofuran ring of the reduced furanochroman subunit of phomactin A. The strategy utilizes the O-TBS-protected 3-epoxy-(3 -hydroxy ketone 201. Cleavage with TBAF starts the retro-... 

The field of alkaloid synthesis via tandem cyclizations favors the application of (TMSlsSiH over other radical-based reagents, due to its very low toxicity and high chemoselectivity. For example, cyclization of the iodoarylazide 102, mediated by (TMSlsSiH under standard experimental conditions, produced the N-Si(TMS)3 protected alkaloid 103 that after washing with dilute acid afforded the amine 104 in an overall 83% yield from 102 (Reaction 81). ° The formation of the labile N-Si(TMS)3 bond was thought to arise from the reaction of the product amine 104 with the by-product (TMSlsSil. The skeletons of ( )-horsfiline, ( )-aspidospermidine and (+ )-vindoline have been achieved by this route. - ... 

Telomeres are the nucleoprotein assembUes at the ends of chromosomes that comprise guanine-rich tandem-repeating DNA sequences (the size of a typical telomere is aroimd 6-12 kb in length in hiunans) together with a number of structural and regulatory proteins. The major function of telomeres is to protect chromosome ends from base-pair loss and end-to-end fusions, thereby safeguarding the integrity of each chromosome [10, llj. The enzyme... 

Maximum residue limit Mass spectrometry Tandem mass spectrometry Material safety data sheet North American Free Trade Act N-Hydroxysuccinimide Nitrogen-phosphorus detection Neomycin phosphotransferase II Optical density Office of Plant Protection and Quarantine... 

Both RCRA and CERCLA contain provisions that allow U.S. EPA to require persons contributing to an imminent hazard to take the necessary actions to clean up releases. RCRA s imminent and substantial endangerment provision addresses nonhazardous as well as hazardous solid waste releases. The authority under CERCLA is essentially the same, except that CERCLA s authority to abate an imminent or substantial danger to public health or the environment is limited to hazardous substance releases. In an enforcement action, the RCRA and CERCLA imminent hazard provisions may be used in tandem to ensure adequate protection of human health and the environment. 

A tandem enolate-arylation-allylic cyclisation, in which an essential z-butyldimethylsilyl ether protecting group delays the cyclisation step until the Pd-catalysed arylation is complete, enables 1-vinyl-l//-[2]benzopyrans 54 to be prepared from 2-bromobenzaldehyde (Scheme 32) <00CC1675>. 4-Substituted isochromans 55 are formed from aldehydes by a Pd-catalysed termolecular queuing cascade. The sequence involves cyclisation of an aryl iodide onto a proximate alkyne followed by an allene insertion. Transmetallation with indium then allows addition to the aldehyde (Scheme 33) . 

Tandem Sonogashira reactions starting with iodopyrrole 122 have furnished the dipyrrolylacetylene 124, and dimerization of 123 gives 125 [86], The Sonogashira coupling has also been reported for enol triflate 55 reacting with an /V-protected propargyl amine [81]. 

Richardson SD, Thruston AD, McGuire JM, Weber EJ (1993) Structural characterization of reactive dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry. Environmental Protection Agency (EPA) Rep EPA600J93423, p 99... 

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