A Five-Step Synthesis of (±)-Tylophorine via a Nitrile-Stabilized Ammonium Ylide

The Stevens rearrangement of a nitrile-stabilized ammonium ylide is the key step of a very short and practical synthesis of the phenanthroindolizine alkaloid (±)-tylophorine. The method requires only five linear steps and is devoid of any protecting group manipulations.     

6‐Methoxy‐2‐oxo‐1,2‐dihydroquinoline‐3,4‐dicarbonitriles,A Red Compound Class with Solvent and pH Independent Green Fluorescence Maxima

The sodium p‐toluenesulfinate mediated reaction of potassium cyanide with 4‐chlorocarbostyrils 8 , 16 , 18 , and 23 gave in all cases the highly fluorescent and stable 6‐methoxy‐2‐oxoquinoline‐3,4‐dicarbonitrile 9 (λ_exc 460 nm and λ_em 545 nm). This is remarkable, because starting carbostyrils 8 , 16 , 18 , and 23 had a chloro substituent, a nitro substituent, an acetylamino substituent, or a piperidinyl substituent in position 3. Hence, we observed not only a substitution of the 4‐chloro and expected 3‐chloro substituents by the cyanide nucleophile but also an exchange of a nitro substituent, an acetylamino substituent, and a piperidinyl substituent in position 3. The multistep insertion of substituents leading to 8 , 16 , 18 , and 23 started from 4‐hydroxy‐6‐methoxyquinolone 4 , easily obtained from p‐anisidine and malonic acid. Substitutions in position 3 gave 4‐hydroxy‐3‐nitro and 3‐chloro intermediates, which were converted to 3,4‐dichlorocarbostyril 8 and 4‐chloro‐3‐nitrocarbostyril 16 . Reduction of the 3‐nitro intermediate led to the 3‐acetylamino analog and subsequent chlorination led to 3‐acetylamino‐4‐chlorocarbostyril 18 . 4‐Chloro‐3‐piperidinylcarbostyril 23 was obtained from intermediate 3,3‐dichloroquinolinedione by subsequent amination, reduction and chlorination. Further, 3‐acetylamino‐4‐chlorocarbostyril 18 gave with lithium p‐toluenesulfinate highly fluorescent 3‐amino‐6‐methoxy‐4‐p‐tolylsulfonylquinolone 19 .     

Comparison of isoscalar and isovector (e,e′) M1 form factors at high momentum transfer

Electron scattering M1 form factors have been measured for the ground state and for the 2.313 MeV M1 transition in ¹⁴N. Whereas the ground-state form factor is in good accord with 1p-shell models, the data for the 2.313 MeV transition show an unexplained enhancement at high momentum transfers.     

Rapid identification of substrates for novel proteases using a combinatorial peptide library

Fluorogenic substrates for assaying novel proteolytic enzymes could be rapidly identified using an easy, solid-phase combinatorial assay technology. The methodology was validated with leader peptidase of Escherichia coli using a subset of an intramolecularly quenched fluorogenic peptide library. The technique was extended toward the discovery of substrates for a new aspartic protease of pharmaceutical relevance (human napsin A). We demonstrated for the first time known to us that potent fluorogenic substrates can be discovered using extracts of cells expressing recombinant enzyme to screen the peptide library. The straightforward and rapid optimization of protease substrates greatly facilitates the drug discovery process by speeding up the development of high throughput screening assays and thus helps more effective exploitation of the enormous body of information and chemical structures emerging from genomics and combinatorial chemistry technologies.     

Mass spectrometry: a tool for the identification of proteins separated by gels

Mass spectrometry (MS) has become the technique of choice to identify proteins. This has been largely accomplished by the combination of high-resolution two-dimensional (2-D) gel separation with robotic sample preparation, automated MS measurement, data analysis, and database query. Developments during the last five years in MS associated with protein gel separation are reviewed.