Michael Reactions of α-Unsubstituted Trisubstituted 1H-Pyrroles

To obtain stable derivatives of α-unsubstituted pyrroles, the reaction of the test pyrrole 9 with a series of chalcones 14a – h were studied. Michael adducts 16b – h could be isolated. In order to synthesize coloured derivatives, the reaction of different pyrroles 9, 21, 23 , and 25 with diphenylpropynone 19 was investigated. In these cases, too, Michael-addition products were formed. The intense absorption band around 400 nm makes the identification of these derivatives easy.     

rac‐(Z)‐Ethyl 2‐bromo‐2‐[(3R,5R)‐3‐bromo‐5‐methyl­tetra­hydro­furan‐2‐yl­idene]acetate

In the title compound, C₉H₁₂Br₂O₃, a (tetra­hydro­furan‐2‐yl­idene)acetate, the double bond has the Z form. In the tetra­hydro­furan group, the relative configuration of the Br atom in the 3‐position and the methyl group in the 5‐position is anti. The compound crystallizes with two independent mol­ecules per asymmetric unit and, in the crystal structure, the individual mol­ecules are linked to their symmetry‐equivalent mol­ecules by C—H⋯O hydrogen bonds, so forming centrosymmetric hydrogen‐bonded dimers.     

Die röntgenstrukturanalysen von (E)- und (Z)-2-Buten-1,4-diyl-dithiocyanat bei 93 K

The X-Ray Diffraction Analysis of (E)- and (Z)-2-Butene-1,4-diyl Dithiocyanate The crystal structure of the (E)- and (Z)-2-butene-1,4-diyl dithiocyanate ( 1 and 2 , respectively) which have been used as substrates for an E′ reaction, has been determined by X-ray analysis. The SCN groups are for both molecules in an anticlinal conformation relative to the double bond. A remarkable intermoecular contact has been observed between the N-atom of one molecule and the S-atom of its neighbour.     

Determination of intracellular prolyl/glycyl proteases in intact living human cells and protoporphyrin IX production as a reporter system

The determination of enzyme activity or inhibition in intact living cells is a problem in the development of inhibitors for intracellular proteases. The production of fluorescent protoporphyrin IX (PpIX) from the nonfluorescent (N)-Gly/Pro-5-aminolevulinic acid (ALA) substrates was used to evaluate the prolyl/glycyl-specific dipeptidylpeptidase IV (DPPIV)-like and prolyloligopeptidase (POP)-like activities of human cells. The results demonstrated that whereas POP-like activity could be attributed to the actual POP, the DPPIV-like activity could be related to actual DPPIV only in one colon cell line. In the other breast and colon cell lines, DPPIV-like activity was intracellular and displayed by other prolyl-specific aminopeptidases. Our experiments also demonstrated the involvement of glycyl-specific proteases in the processing of ALA precursors. These observations have important consequences for the development and evaluation of selective inhibitors for these enzymes.     

Facile synthesis of a "ready to use" precursor of porphobilinogen and its amino Acid derivatives

A practical synthesis of porphobilinogen based on the biosynthetic mechanism is described. The crossed Mukayiama aldol reaction is the key step creating the central carbon-carbon bond between the two protected forms of 5-aminolevulinic acids. The optimized sequence gives a crystalline, storable precursor, which can be transformed in high yield into porphobilinogen and bioconjugates thereof. The enzymatic hydrolysis of the precursor produces porphobilinogen in quantitative yield.     

Inhibition of Escherichia coli porphobilinogen synthase using analogs of postulated intermediates

BACKGROUND: Porphobilinogen synthase is the second enzyme involved in the biosynthesis of natural tetrapyrrolic compounds, and condenses two molecules of 5-aminolevulinic acid (ALA) through a nonsymmetrical pathway to form porphobilinogen. Each substrate is recognized individually at two different active site positions to be regioselectively introduced into the product. According to pulse-labeling experiments, the substrate forming the propionic acid sidechain of porphobilinogen is recognized first. Two different mechanisms for the first bond-forming step between the two substrates have been proposed. The first involves carbon-carbon bond formation (an aldol-type reaction) and the second carbon-nitrogen bond formation, leading to an iminium ion. RESULTS: With the help of kinetic studies, we determined the Michaelis constants for each substrate recognition site. These results explain the Michaelis-Menten behavior of substrate analog inhibitors - they act as competitive inhibitors. Under standard conditions, however, another set of inhibitors demonstrates uncompetitive, mixed, pure irreversible, slow-binding or even quasi-irreversible inhibition behavior. CONCLUSIONS: Analysis of the different classes of inhibition behavior allowed us to make a correlation between the type of inhibition and a specific site of interaction. Analyzing the inhibition behavior of analogs of postulated intermediates strongly suggests that carbon-nitrogen bond formation occurs first.