Investigation of chiral reactions: the structural detection of new hydrogenated isocinchona alkaloids from mixtures without isolation using electrospray ionization tandem mass spectrometry

Abstract

The reaction mixture for the hydrogenation of ethyl pyruvate on Pt-alumina catalyst modified with isocinchona alkaloids (alpha-ICN (I) and beta-ICN (II)) was studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). It was established that part of the chiral modifiers themselves are converted into ions of m/z 299, 305 and 309 in the course of chiral hydrogenation. The experimental data allowed the determination of the probable structure of the ions mentioned. According to ESI-MS/MS spectra the structure of the new cinchona alkaloids was assumed: tetrahydro-isocinchonines (III-VI), decahydro-isocinchonines (VII, VIII) and hydrogenated compounds of VII and VIII by scission of their C--N and C--O bonds (IX/1, IX/2, X). Fragmentation pathways are proposed for these new compounds.

Anomalous behavior of rigid cinchona alkaloids in the enantioselective hydrogenation of ethyl pyruvate in an aprotic solvent

“…The observed slight decrease of ee at high conversion (see data given Table 1 and results given in Fig. 3A and B) is due to the loss of CD or CN, because of the hydrogenation of their quinoline ring [43,44]. As emerges from Fig.…”

“…In earlier studies based on kinetic, NMR and circular dichroism results [14,17,20,33,34,36] and ESI-MS investigation [48] the formation of substrate-modifier complex in the liquid phase has been proved. Literature analogies [49,50] and our molecular modeling, related molecular mechanics calculations [17,18,20] and results obtained using nano-sized colloidal Pt [21] provided further proof that the closed conformer of CD (or CN) can be involved in the formation of the substratemodifier complex.…”

“…5) might indicate the loss of the alkaloid in the hydrogenation reaction. As already mentioned this loss is due to the hydrogenation of the quinoline ring [43,44]. We suggest that owing to the rigid structure these alkaloids can be more easily accommodated at the Pt surface than the flexible CD or CN.…”

Heterogeneous Catalytic Enantioselective Hydrogenation of Activated Ketones

“…A comparison of the hydrogenation of isocinchonas with those of CD and DHCD shows that the quinoline skeleton of α-and β-ICN are hydrogenated considerably faster. [113,114] helped to determine the probability of the structures outlined in Fig. (39).…”

“…(3)). ESI-MS was our method of choice for studying the conversions of α-ICN and β-ICN under hydrogenative conditions [113,114,242].…”