Synthesis and reactivity of enantiomerically pure N-alkyl-2-alkenyl azetidinium salts

Rhodium-Catalyzed One-Carbon Ring Expansion of Aziridines with Vinyl-N-triftosylhydrazones for the Synthesis of 2-Vinyl Azetidines

Azetidines, being four-membered N-heterocycles, possess significant potential in contemporary medicinal chemistry owing to their favorable pharmacokinetic properties. Regrettably, the incorporation of functionalized azetidines into pharmaceutical lead structures has been impeded by the absence of efficient synthetic methods for their synthesis. In this study, a Rh-catalyzed one-carbon ring expansion of aziridines with vinyl-N-triftosylhydrazones is presented, which facilitates the synthesis of high value-added 2-alkenyl azetidine products. This research represents the first example of ring expansion of aziridines enabled by vinyl carbenes. Additionally, a one-pot two-step protocol, initiated from cinnamaldehyde, was successfully achieved, offering a step-economical and facile approach for the synthesis of these compounds. The pivotal aspect of this successful transformation lies in the in situ formation of an alkenyl aziridinium ylide intermediate. Experimental investigations, coupled with computational studies, suggest that a diradical pathway is involved in the reaction mechanism.

Biocatalytic One-Carbon Ring Expansion of Aziridines to Azetidines via a Highly Enantioselective [1,2]-Stevens Rearrangement

We report enantioselective one-carbon ring expansion of aziridines to make azetidines as a new-to-nature activity of engineered "carbene transferase" enzymes. A laboratory-evolved variant of cytochrome P450_BM3, P411-AzetS, not only exerts unparalleled stereocontrol (99:1 er) over a [1,2]-Stevens rearrangement but also overrides the inherent reactivity of aziridinium ylides, cheletropic extrusion of olefins, to perform a [1,2]-Stevens rearrangement. By controlling the fate of the highly reactive aziridinium ylide intermediates, these evolvable biocatalysts promote a transformation which cannot currently be performed using other catalyst classes.

Base-promoted diastereoselective α-alkylation of borane N-((S)-1'-phenylethyl)azetidine-2-carboxylic acid ester complexes

The base-promoted α-alkylation of N-((S)-1-phenylethyl)azetidine-2-carboxylic acid esters 1 was investigated. The use of diastereomerically pure borane complexes 3 as substrates, which are easily prepared from 1, dramatically improved the yields and diastereoselectivities of α-alkylated products 2. For example, the treatment of tert-butyl ester (1S,2S,1'S)-3a with 2.4 equivalents of lithium bis(trimethysilyl)amide (LiHMDS) at 0 °C followed by 2.6 equivalents of benzyl bromide afforded α-benzylated (2S,1'S)-2aa in 90% yield as almost a single diastereomer. Our method enables the production of optically active α-substituted azetidine-2-carboxylic acid esters starting from commercially available (S)-1-phenylethylamine, which is one of the least expensive chiral compounds.

Structural and mechanistic studies of the base-induced Sommelet–Hauser rearrangement of N-α-branched benzylic azetidine-2-carboxylic acid-derived ammonium salts

The base-induced Sommelet–Hauser rearrangement of N-α-branched benzylic azetidine-2-carboxylic acid ester-derived ammonium salts was demonstrated.

Bisethylnorspermine lipopolyamine as potential delivery vector for combination drug/gene anticancer therapies

PURPOSE

To design novel synthetic gene delivery system in which the carrier molecule functions dually as a carrier and a cytotoxic agent targeting dysregulated polyamine metabolism in cancer.

METHODS

Bisethylnorspermine (BENSpm) lipopolyamine was synthesized and its toxicity evaluated by MTS assay in MCF-7 and MCF-10A cells. Transfection activity was determined using luciferase plasmid DNA.

RESULTS

Asymmetrical lipid analogue of polyamine anticancer drug BENSpm was synthesized using nucleophilic ring opening of azetidinium ion. The synthesized LipoBENSpm showed cytotoxicity comparable to that of parent BENSpm in human breast cancer cell line MCF-7 but mediated 3-4 orders magnitude higher transfection activity. Importantly, cytostatic activity of BENSpm, typically in a low muM range, falls within a relevant and typical concentration range required for efficient gene delivery.

CONCLUSIONS

These findings make gene delivery vectors based on BENSpm promising candidates for combination drug/gene approaches to the treatment of cancer.

3-Aminopyrrolidines via Ring Rearrangement of 2-Aminomethylazetidines. Synthesis of (−)-Absouline

[reaction: see text] A new entry to enantiopure 3-aminopyrrolidines was developed using a boron trifluoride-mediated rearrangement of 2-aminomethylazetidines. The method is quite general and produces rearranged products in good yield regardless of both substitution pattern and relative stereochemistry of the starting material. A concise stereocontrolled synthesis of (-)-absouline was achieved on the basis of this new method.