Catalytic Asymmetric Synthesis of Alkynyl Aziridines: Both Enantiomers of cis ‐Aziridines from One Enantiomer of the Catalyst

Halogenated monopyridinium oximes are less effective in reactivation of phosphylated cholinesterases than bisquaternary oximes

Mono-quaternary pyridinium oximes derived from K-oximes K027, K048 and K203 were designed, synthesized and evaluated for the reactivation of organophosphate-inhibited cholinesterases. The incorporation of the halogen atoms to the structure decreased the pKa value of the oxime group resulting in an increased formation of oximate necessary for reactivation. The stability and pKa values were found to be similar to analogous bis-quaternary compounds. Some mono-quaternary oximes resulted as relatively strong inhibitors of human acetylcholinesterase. Nevertheless, the reactivation ability of mono-quaternary oximes for organophosphate-inhibited cholinesterases was lower compared to their bis-quaternary analogues. These results were further confirmed by the determination of reactivation kinetics, when in some cases novel compounds showed improvement reactivation compared to the tested standards, but no improvement to bis-quaternary K-oximes. A computational study investigated reactivation process for K027, and its two analogues for VX-inhibited AChE. This study revealed slight differences between reactivation of mono-quaternary and bis-quaternary oximes. Abbreviations: 2-PAM, pralidoxime; AChE, acetylcholinesterase; ACN, acetonitrile; ATCI, acetylcholine iodide; BChE, butyrylcholinesterase; BTCI, butyrylcholine iodide; Bu3SnSnBu3, bis(tributyltin) Et2O, diethyl ether; ChEs, cholinesterases; CNS, central nervous system; DAD, diode array detector; DIBAL-H, diisobutylaluminium hydride; DMF, dimethylformamide; DMSO, dimethyl sulfoxide; DTNB, 5,5́-dithiobis-2-nitrobenzoic acid; Et3N, triethylamine; EtOAc, ethyl acetate; EWG, electron withdrawing group; HI-6, asoxime; hrAChE, human recombinant acetylcholinesterase; hrBChE, human recombinant butyrylcholinesterase; hrChEs, human recombinant cholinesterases; HPLC, high-performance liquid chromatography; HRMS, high-resolution mass spectrometry; KD, dissociation constant; kr, first-order reactivation rate constant; kr2, second-order reactivation rate constant; LüH-6, obidoxime; MeOH, methanol; MM, molecular mechanics; MMC-4, methoxime; m.p., melting point; NCIs, non-covalent interactions; NEDPA, 4-nitrophenyl ethyl dimethylphosphoramidate; NEMP, 4-nitrophenyl ethyl methylphosphonate; NIMP, isopropyl methylphosphonate; NMR, nuclear magnetic resonance spectroscopy; OPs, organophosphates; PBS, phosphate-buffered saline; Pd(dppf)Cl2.CH2Cl2, [1,1'-Bis(diphenylphosphino)ferrocene]dichloropalladium(II) in complex with dichloromethane; pKa, negative decimal logarithm of the dissociation constant; POX, paraoxon; PPh3, triphenylphosphine; QM, quantum mechanics; rt, room temperature; SN2, bimolecular nucleophilic substitution; SNAc, nucleophilic acyl substitution; THF, tetrahydrofuran; TMC-4, trimedoxime; TNB, 5-thio-2-nitrobenzoic acid; UHPLC, ultra high-performance liquid chromatography; UV, ultraviolet; UV-VIS, ultraviolet-visible.

Fluorinated triazole-containing sphingosine analogues. Syntheses and in vitro evaluation as SPHK inhibitors

Sphingosine analogues with a rigid triazole moiety in the aliphatic chain and systematic modifications in the polar head and different degrees of fluorination at the terminus of the alkylic chain were synthesized from a common alkynyl aziridine key synthon. This key synthon was obtained by enantioselective organocatalyzed aziridination and it was subsequently ring opened in a regioselective manner in acidic medium. Up to 16 sphingosine analogues were prepared in a straightforward manner. The in vitro activity of the obtained products as SPHK1 and SPHK2 inhibitors was evaluated, displaying comparable activity to that of DMS.

Multicomponent Catalytic Asymmetric Synthesis of trans-Aziridines

A multicomponent trans-aziridination of aldehydes, amines, and diazo compounds with BOROX catalysts is developed. The optimal protocol is slightly different for aryl aldehydes than for aliphatic aldehydes. The key to the success with aryl aldehydes was allowing the catalyst, aldehyde, and amine to react for 20 min before addition of the diazo compound. A variety of 11 different electron-poor and electron-rich aryl aldehydes were screened to give trans-aziridines in 73-90% yield with 82-99% ee and trans/cis selectivities of 19:1 to >99:1. The optimal protocol for the trans-aziridination of aliphatic aldehydes did not require prereaction of the catalyst, aldehyde, and amine, and instead, the diazo compound could be added directly. The scope of the reaction is limited to unbranched aliphatic aldehydes and was tolerant of a number of functional groups including ethers, esters, epoxides, carbamates, and phthalimides. A total of 10 aliphatic aldehydes were examined and found to give trans-aziridines in 60-88% yield with 60-98% ee and trans/cis selectivities of 6:1 to >99:1. Alkenyl aldehydes did not react, but an alkynyl aldehyde gave a 71% yield and 95% ee of an aziridine that was found to be the cis- and not the trans-diastereomer. The aryl and aliphatic aldehydes both gave the trans-aziridines with the same absolute configuration with the same catalyst; however, in those cases where cis-aziridines were formed, the configuration was opposite for those formed from aryl versus aliphatic aldehydes.

Brønsted Base-Mediated Aziridination of 2-Alkyl-Substituted-1,3-Dicarbonyl Compounds and 2-Acyl-Substituted-1,4-Dicarbonyl Compounds by Iminoiodanes

The synthesis of α,α-diacylaziridines and α,α,β-triacylaziridines from reaction of 2-alkyl-substituted-1,3-dicarbonyl compounds and 2-acyl-substituted-1,4-dicarbonyl compounds with arylsulfonyliminoiodinanes (ArSO2N=IPh) under Brønsted base-mediated atmospheric conditions is described. The reaction mechanism is thought to involve the formal oxidation of the substrate followed by aziridination of the ensuing α,β-unsaturated intermediate by the hypervalent iodine(iii) reagent.