Aziridines

Aziridines are useful intermediates and pharmaceuticals. Therefore there is a growing need for their environmentally benign production. [1] Many olefin aziridinations rely on the addition of nitrenes, which are generated by either thermal or photochemical azide decomposition or are formed in situ from tosylimino phenyliodinane, sulfonyl azides, or chloramine-T using metal catalysts. [2] Halogens have also been proposed as catalysts in combination with chloramine-T, which is both a strong nucleophile and an oxidant. [3] In this route, pioneered by Sharpless [3a] and Komatsu, [3b] reaction of the oxidized halogen ("Br + ", "I + ") with the double bond is followed by nucleophilic attack of chloramine-T and cyclization. The main drawback of all previous reactions is the use of complex nitrogen-containing sources, which lead to N-substituted aziridines that require a subsequent deprotection step. Direct routes from olefins to unprotected aziridines have only been described for a,b-unsaturated carbonyl compounds and often require complex NH donors. Ammonia, which is the most obvious nucleophilic nitrogen source, has barely been considered in aziridinations. Only the Gabriel-Cromwell aziridination uses NH 3 , but the scope of this reaction is restricted to a,b-unsaturated a-halocarbonyl compounds. [5a,b] The direct incorporation of ammonia into olefins is therefore justly recognized as a top priority for catalysis. [6] Herein we describe the first successful catalytic synthesis of unprotected aziridines from NH 3 and simple olefins. Our method resembles a halide-assisted epoxidation, in which the olefin is attacked by "Br + " cation, which is formed in situ by oxidation of bromide, and then by water as the oxygen source. The resulting bromohydrin is then cyclized to the epoxide. As will be shown, a similar concept can be applied for the N-functionalization of styrenes by replacing water with ammonia as the nucleophile: unprotected aziridines are formed in a one-pot, micellar system using iodide as a catalyst, aqueous bleach as an oxidant, and ammonia as the nitrogen source [Eq. (1)].

Spores of some species of the strictly anaerobic bacteria Clostridium naturally target and partially lyse the hypoxic cores of tumors, which tend to be refractory to conventional therapies. The anti-tumor effect can be augmented by engineering strains to convert a non-toxic prodrug into a cytotoxic drug specifically at the tumor site by expressing a prodrug-converting enzyme (PCE). Safe doses of the favored prodrug CB1954 lead to peak concentrations of 6.3 µM in patient sera, but at these concentration(s) known nitroreductase (NTR) PCEs for this prodrug show low activity. Furthermore, efficacious and safe Clostridium strains that stably express a PCE have not been reported. Here we identify a novel nitroreductase from Neisseria meningitidis, NmeNTR, which is able to activate CB1954 at clinically-achievable serum concentrations. An NmeNTR expression cassette, which does not contain an antibiotic resistance marker, was stably localized to the chromosome of Clostridium sporogenes using...

Dedicated to Professor Tae Young Lee on the occasion of his 90th birthday CH 3 CN to afford either piperidines or pyrrolidines through regio-and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring-opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways. Scheme 1. Formation of a) monocyclic and b) bicyclic aziridinium ions and their subsequent ring-opening reactions by nucleophiles.