A Cascade Aza-Cope/Aza-Prins Cyclization Leading to Piperidine Derivatives

Stereoselective synthesis of 1,6-diazecanes by a tandem aza-Prins type dimerization and cyclization process

We report the stereocontrolled synthesis of 1,6-diazecanes via a tandem aza-Prins type reaction of N-acyliminium ions with allylsilanes. It involves an aza-Prins type dimerization and cyclization in a single-step operation. This reaction represents the first example of 10-membered N-heterocycle synthesis using an aza-Prins reaction. Also, the interesting formation of an unusual tetracyclic compound through further cyclization of 1,6-diazecane and bicyclic compounds by the intramolecular cyclization of linear allylsilane are described. This tandem aza-Prins protocol provides a new synthetic strategy for the direct synthesis of medium-sized nitrogen heterocycles.

Click and Cut: a click chemistry approach to developing oxidative DNA damaging agents

Metallodrugs provide important first-line treatment against various forms of human cancer. To overcome chemotherapeutic resistance and widen treatment possibilities, new agents with improved or alternative modes of action are highly sought after. Here, we present a click chemistry strategy for developing DNA damaging metallodrugs. The approach involves the development of a series of polyamine ligands where three primary, secondary or tertiary alkyne-amines were selected and 'clicked' using the copper-catalysed azide-alkyne cycloaddition reaction to a 1,3,5-azide mesitylene core to produce a family of compounds we call the 'Tri-Click' (TC) series. From the isolated library, one dominant ligand (TC1) emerged as a high-affinity copper(II) binding agent with potent DNA recognition and damaging properties. Using a range of in vitro biophysical and molecular techniques-including free radical scavengers, spin trapping antioxidants and base excision repair (BER) enzymes-the oxidative DNA damaging mechanism of copper-bound TC1 was elucidated. This activity was then compared to intracellular results obtained from peripheral blood mononuclear cells exposed to Cu(II)-TC1 where use of BER enzymes and fluorescently modified dNTPs enabled the characterisation and quantification of genomic DNA lesions produced by the complex. The approach can serve as a new avenue for the design of DNA damaging agents with unique activity profiles.

Synthetic Factors Governing Access to Tris(β-diketimine) Cyclophanes versus Tripodal Tri-β-aminoenones

Tris(β-diketimine) cyclophanes are an important ligand class for investigating cooperative multimetallic interactions of bioinorganic clusters. Discussed herein are the synthetic factors governing access to tris(β-diketimine) cyclophanes versus tripodal tri-β-aminoenones. Cyclophanes bearing Me, Et, and MeO cap substituents and β-Me, Et, or Ph arm substituents are obtained, and a modified condensation method produced α-Me β-Me cyclophane. These operationally simple procedures produce the ligands in gram quantities and in 22-94% yields.

A 5 + 1 Protic Acid Assisted Aza-Pummerer Approach for Synthesis of 4-Chloropiperidines from Homoallylic Amines

We report that HCl·DMPU induces the formation of (thiomethyl)methyl carbenium ion from DMSO under mild conditions. Homoallylic amines react with this electrophile to generate 4-chloropiperidines in good yields. The method applies to both aromatic and aliphatic amines. The use of HCl·DMPU as both non-nucleophilic base and chloride source constitutes an environmentally benign alternative for piperidine formation. The reaction has a broad substrate scope, and the conditions offer good chemical yields with high functional group tolerance and scalability.

Acetic acid-promoted cascade N-acyliminium ion/aza-Prins cyclization: stereoselective synthesis of functionalized fused tricyclic piperidines

A novel acetic acid-promoted metal-free cascade N-acyliminium ion/aza-Prins cyclization of o-formyl carbamates and homoallylamines is reported. This one-pot protocol provides efficient and rapid access to masked cis-hydroxyhexahydropyrido[1,2-c]quinazolin-6-ones with concomitant generation of two stereogenic centers, four C-C/C-O/C-N bonds and two new rings in good yield and excellent diastereoselectivity.

A protecting-group-free synthesis of (+)-nephrosteranic, (+)-protolichesterinic, (+)-nephrosterinic, (+)-phaseolinic, (+)-rocellaric acids and (+)-methylenolactocin

A collective synthesis of a γ-butyrolactone class of paraconic acids such as (+)-methylenolactocin, (+)-phaseolinic acid, (+)-nephrosteranic acid, (+)-nephrosterinic acid, (+)-rocellaric acid and (+)-protolichesterinic acid is described.

Unimolecular tetrakis-piperidine-4-ol: an efficient ligand for copper and amine free Sonogashira coupling

Unimolecular tetrakis-4-hydroxypiperidine catalysed Cu and amine free Sonogashira coupling of various aryliodides/bromides and alkyl or aryl terminal alkynes giving access to internal arylalkynes is reported.