RESUMO
Multiply permanently charged analytes (MPCAs) are of great interest for various applications. MPCA soft ionization mass spectra (MS) strongly depend on the counterions of MPCA. We have studied thoroughly this effect to expand the use of MS in MPCA characterization. To this end, ß-cyclodextrin-based MPCAs with 7 (MIM7NBCD) and 14 (MIM14BCD) quaternary ammonium charges with a series of monovalent counterions were prepared and their MS were measured using two of the most popular soft ionization techniques, electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI). MALDI MS of both analytes were well resolved, with signals assignable to the analytes only with the two least basic tested counterions (ClO4- and TfO-). Similarly, analyte-assignable signals were observed in ESI MS of MIM14BCD only with ClO4- and TfO-. The situation was opposite with ESI MS of MIM7NBCD where assignable signals were observed with Cl- but not with TfO-. Thus, to get high-quality MS, binding between the MPCA permanent charges and the counterions must be of the optimal effective strength, given also by the number of analyte permanent charges as shown by the simple combinatorial model of binding. Of practical interest is the observation that unsuitable counterions can be replaced in situ by an excess of corresponding acid. The findings form a coherent framework for interpreting and improving MPCA mass spectra.
RESUMO
The first continuous flow method was developed for the synthesis of 6-monoamino-6-monodeoxy-ß-cyclodextrin starting from native ß-cyclodextrin through three reaction steps, such as monotosylation, azidation and reduction. All reaction steps were studied separately and optimized under continuous flow conditions. After the optimization, the reaction steps were coupled in a semi-continuous flow system, since a solvent exchange had to be performed after the tosylation. However, the azidation and the reduction steps were compatible to be coupled in one flow system obtaining 6-monoamino-6-monodeoxy-ß-cyclodextrin in a high yield. Our flow method developed is safer and faster than the batch approaches.
RESUMO
Ammonium salt derivatives with a neopentyl moiety are remarkably stable against Hofmann elimination, but the neopentyl moiety slows nucleophilic substitution, complicating their synthesis. To identify the best leaving group for the synthesis of the ammonium salts, we prepared six 1,1,1-tris(X-methyl)ethane derivatives, where X is chloride, bromide, iodide, methanesulfonate, p-toluenesulfonate, and trifluoromethanesulfonate (triflate), and studied the kinetics of their reactions with sodium, cesium, or tetramethylammonium azide in deuterated dimethylsulfoxide (DMSO) at 100 °C by NMR spectroscopy. Iodide and bromide were found to be more reactive than p-toluenesulfonate and methanesulfonate. As expected, the best leaving group for nucleophilic substitution was triflate. Despite the usual high reactivity and instability of primary alkyl triflates, neopentyl triflate can be used as a stable but sufficiently reactive reactant for nucleophilic substitution on neopentyl skeletons.
RESUMO
Cyclodextrins are well known supramolecular hosts used in a wide range of applications. Monosubstitution of native cyclodextrins in the position C-6 of a glucose unit represents the simplest method how to achieve covalent binding of a well-defined host unit into the more complicated systems. These derivatives are relatively easy to prepare; that is why the number of publications describing their preparations exceeds 1400, and the reported synthetic methods are often very similar. Nevertheless, it might be very demanding to decide which of the published methods is the best one for the intended purpose. In the review, we aim to present only the most useful and well-described methods for preparing different types of mono-6-substituted derivatives. We also discuss the common problems encountered during their syntheses and suggest their optimal solutions.