The 1,3 O→C silyl rearrangement of silyl enol ether anions - synthesis of α-silyl ketones

Silyl enol ethers with sterically hindered silyl groups are transformed into the corresponding α-silyl ketones by treatment with n-butyllithium/potassium tert-butylate.     

Regiospecific synthesis of (±)-deoxyanthracyclinones

A versatile regiospecific route to tetracyclic anthracyclinones is described; the synthetic strategy entails the attachment of a nucleophilic C-D ring synthon, $\text{2b}$, to a suitably functionalized A ring intermediate such as $\text{3}$.     

Synthesis of two position isomers of leukotriene C having the S-peptide at C(12)

Two positional isomers of leukotriene C(1) (4a,4b), previously considered as possibly being members of the family of slow reacting substances, have been synthesized and found to be biologically inactive.     

Short, enantioselective total synthesis of aflatoxin B2 using an asymmetric [3+2]-cycloaddition step

A highly enantioselective [3+2]-cycloaddition reaction of 2,3-dihydrofuran with 1,4-benzoquinones using a chiral oxazaborolidinium triflimidate as catalyst has been developed which allows rapid access to a variety of chiral phenolic tricycles (enantiomeric excesses ranging from 91 to 98%). The utility of this new methodology is demonstrated by a short synthesis of the important pentacyclic natural product, aflatoxin B2. This exploratory study indicates that an even broader application of these catalysts to enantioselective cycloadditions may be possible.     

Catalysis of enantioselective [2+1]-cycloaddition reactions of ethyl diazoacetate and terminal acetylenes using mixed-ligand complexes of the series Rh2(RCO2)n(L*4-n). Stereochemical heuristics for ligand exchange and catalyst synthesis

This paper describes the synthesis of mixed Rh(2)(II) complexes containing bridging acetate and R,R-diphenyl-N-triflylimidazolidinone (DPTI) ligands (1, 2, and 9-19), and their function as enantioselective catalysts for the conversion of ethyl diazoacetate and terminal acetylenes to chiral cyclopropenes. Of these catalysts, 1 and 10 functioned with the highest enantioselectivity, in accord with a mechanistic model in which one of the ligand bridges is broken in the intermediate Rh-carbene complex. The synthetic results allow conclusions with regard to kinetically and thermodynamically favored pathways for the synthesis of mixed acetate-DPTI complexes. A new C(2)-symmetric complex having only two anti-DTBTI bridges (23) is shown to be a highly effective chiral catalyst, as expected from the model.     

Increasing peptide identification in tandem mass spectrometry through automatic function switching optimization

Comprehensive proteomic studies that employ MS directed peptide sequencing are limited by optimal peptide separation and MS and tandem MS data acquisition routines. To identify the optimal parameters for data acquisition, we developed a system that models the automatic function switching behavior of a mass spectrometer using an MS-only dataset. Simulations were conducted to characterize the number and the quality of simulated fragmentation as a function of the data acquisition routines and used to construct operating curves defining tandem mass spectra quality and the number of peptides fragmented. Results demonstrated that one could optimize for quality or quantity, with the number of peptides fragmented decreasing as quality increased. The predicted optimal operating curve indicated that significant improvements can be realized by selecting the appropriate data acquisition parameters. The simulation results were confirmed experimentally by testing 10 LC MS/MS data acquisition parameter sets on an LC-Q-TOF-MS. Database matching of the experimental fragmentation returned peptide scores consistent with the predictions of the model. The results of the simulations of mass spectrometer data acquisition routines reveal an inverse relationship between the quality and the quantity of peptide identifications and predict an optimal operating curve that can be used to select an optimal data acquisition parameter for a given (or any) sample.