Huub Henderickx

A Practical Recycle of a Ligand-Free Palladium Catalyst for Heck Reactions

Ligand-free palladium can be recovered almost quantitatively from Heck reaction mixtures by filtration after its deposition on a carrier such as silica or celite. Subsequently, it is re-activated to its original activity by adding a small amount of iodine or bromine prior to the next reaction cycle. The catalyst results in excellent yields and selectivities, even for the less reactive aryl bromides. A catalytic cycle based on anionic palladium intermediates is proposed.

In-source decay of hyperbranched polyesteramides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Hyperbranched polyesteramides (DA2), prepared from hexahydrophthalic anhydride (D) and diisopropanolamine (A) have been characterized, by use of matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)-MS. MALDI of polyesteramides produces protonated molecules. The spectra show a complex chemical composition distribution and end-group distribution which are mainly composed of two series of homologous oligomers DnAn+1 − mzH2O and DnAn − mH2O, where m = 1–2. Signals from protonated molecules DnAn+1 and DnAn are almost absent in the MALDI spectrum, whereas these ions are responsible for the base peak of DnAn+1 − mH2O and DnAn − mH2O (m = 1–2) clusters in the ESI spectrum. The absence of −OH end-groups signals in the MALDI spectrum is due to a metastable decay of protonated DnAn+1 and DnAn ions in the ion source of the MALDI mass spectrometer prior to ion extraction. In-source decay results in the formation of protonated lower DnAn+1 − mH2O and DnAn − mH2O oligomers and their corresponding neutrals, leading to wrong conclusions concerning the relative end-group distribution as a function of the degree of polymerization and the chemical composition.

Chiral liquid chromatography–mass spectrometry for high-throughput screening of enzymatic racemase activity

In finding suitable biocatalysts for processes in chemical industry, expression libraries are constructed containing typically >10,000 clones. Search for a desired activity is done by examination of all the clones in one or more libraries using a high-throughput screening assay. Here we describe a method for the screening of the enzymatic racemase activity of clones from an expression library on alpha-amino-epsilon-caprolactam (ACL) using a fast chiral LC separation and ionspray-MS as the detection technique. After substrate incubation with S-ACL, the 96-well microplates were centrifuged to remove cell material. The conversion of S-ACL to R-ACL was monitored by quantitation of the R-ACL enantiomer. Separation of the two ACL enantiomers was performed on a Crownpak CR+ column within 1 min. A Gilson 215 autosampler with a 889 multiple injection probe was used for injecting the samples into the LC system. The total analysis time for a 96-well microplate was 56 min. The MS was operated in the positive-ion mode using selected ion monitoring at m/z 129 [M+H]+ of ACL. Using this method over 12,000 samples were analyzed without loss in performance of the system. The LC column remained stable without loss of resolution and the MS system did not show loss in sensitivity throughout the screening. Inter-day reproducibility was within 15%.

Flow injection analysis electrospray ionization mass spectrometry for high-throughput screening of a gene library for amidase activity

In high-throughput screening of gene and mutant libraries, high analysis speeds and short method development times are important factors. Mass spectrometry (MS) is considered to be a generic analytical technique with a relatively short development time. Furthermore, when applying flow injection analysis (FIA) for sample introduction, the requirements for high throughput are met. In this work, the use of a single quadrupole electrospray MS instrument for assaying amidase activity in a gene library is demonstrated. The desired selectivity for measuring the amino acid, the reaction product of the amidase reaction, in the presence of high concentrations of the corresponding amino acid amide substrate was obtained by selective ionization of the amino acid in negative ion mode electrospray. The only sample preparation required was a 200-fold dilution of the reaction mixture. For obtaining quantitative results, a complementary calibration procedure was set up to correct for the change in ionization suppression as a function of conversion. This approach was used to screen a Mycobacterium neoaurum gene library consisting of 11,520 clones with alpha-methylleucine amide as substrate within 24h. Conversion was measured on the [M-H]- species of the corresponding alpha-methylleucine (m/z 144). Five positive clones were detected with a conversion ranging from 0.2% to 3.4%.

Direct formation of an organonitrogen compound from a molybdenum nitrido species

The molybdenum nitrido complex 15NMo[N(R)Ar]3 (where R = C(CD3)2CH3, Ar = 3,5-C6H3Me2) reacted with the anhydride of trifluoroacetic acid at room temperature to afford the correspondent organonitrogen compound in almost quantitative yield without the necessity of using additional reagents to achieve the C-N coupling.