A concise, modular synthesis of chiral peraza-macrocycles using chiral aziridines

Functionalized Polyamine Synthesis with Photoredox Catalysis

Polyamines, such as putrescine and spermidine, are pivotal in various biological processes across living organisms. Despite their significance, structurally modified polyamines offer a less-explored avenue for discovering bioactive compounds. The limitation is attributed to the synthetic difficulty of accessing functionalized polyamines. In this study, we accomplished photoredox-catalyzed functionalization of polyamines to diversify their structure. The rapid functionalization allows attaching fluorophores to the target polyamine, facilitating the development of molecular probes for advancing chemical biology studies.

Synthesis and characterization of chiral aza-macrocycles and study of their enantiomer recognition ability for organo-phosphoric acid and phosphonic acid derivatives by 31P NMR and fluorescence spectroscopy

Two diastereomers of optically active N,O-containing new macrocycles with dual chirality were synthesized and evaluated for chiral discrimination of organo phosphoric and phosphonic acids by ³¹P NMR and fluorescence spectroscopy.

Initial rate kinetic studies show an unexpected influence of para-substituents on the catalytic behaviour of manganese complexes of TMTACN in the epoxidation of styrenes with H2O2

Investigations into the efficacy of a range of enantiomerically pure BINOL additives in the epoxidation of styrene substrates with a number of manganese catalysts prepared from the ligand 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN, using hydrogen peroxide as the oxidant have revealed that there are fundamental differences in reactivity between apparently similar systems. Whilst no asymmetric induction was obtained in the styrene oxide products formed, the data obtained from initial rate kinetic studies appear to be consistent with a number of different catalytically active species operating, the nature of which are profoundly affected by the starting materials used.

Recent advances in catalytic asymmetric epoxidation using the environmentally benign oxidant hydrogen peroxide and its derivatives

There has been a recent drive to develop asymmetric catalytic methods to produce epoxides using environmentally benign oxidants, especially hydrogen peroxide. This critical review discusses the advances that have been made using both metal-based and organocatalytic homogeneous catalysts (142 references).

Synthesis of chiral polyazamacrocycles of variable ring size

Synthesis and structure elucidation of optically active tri-, tetra-, and penta-azamacrocycles having 4-methoxyphenyl pendants are described. Regioselective ring opening of a nosylaziridine with secondary benzyl amines was repeatedly performed to afford the cyclization precursors. Intramolecular N-alkylation of N-(omega-haloalkyl) nosylamide provided tri-, tetra-, and penta-azamacrocycles. On the basis of our study of the tetra-azamacrocycle previously elucidated by X-ray single-crystal analysis and in solution by NMR analysis, we conclude that the tri-azamacrocycle does not mainly have a vase-type conformation because of the steric hindrance of the 4-methoxyphenyl groups but the penta-azamacrocycle has a vase-type conformation in CDCl(3) and in CD(2)Cl(2). The vase-type conformation of the penta-azamacrocycle is, however, not as much stable as that observed in the tetra-azamacrocycle because conformational flexibility of the penta-azamacrocycle was observed in deuterated benzene.

Selectively N-protected enantiopure 2,5-disubstituted piperazines: avoiding the pitfalls in solid-phase Fukuyama-Mitsunobu cyclizations

An efficient solid-phase route to ring-substituted piperazines from O-linked resin-bound (S)-aziridine-2-methanol is described. Regioselective microwave-assisted aminolysis followed by intramolecular Fukuyama-Mitsunobu cyclization constitute the key features of the protocol. Simple piperazines and diazepanes were readily obtained without preceding N-protection of the acyclic intermediate, whereas attempts to extend this protocol to chiral 2,5-disubstituted piperazines failed. Modifications encompassing N-carbamoylation prior to ring-closure were therefore investigated. However, standard carbamoylating agents, for example, Fmoc-Cl and Alloc-Cl tended to give bis-protected by-products. Thus, novel microwave-assisted solid-phase N-protection procedures were developed for efficient introduction of Fmoc, Boc and Alloc groups. The subsequent cyclization proceeded in moderate to excellent yields depending on the bulk of the side chain and type of N-protecting group. This protocol readily provided novel cis- and trans-2,5-disubstituted piperazines displaying a variety of N-protecting group patterns after further on-resin manipulations. Also, unexpected by-products obtained during these optimization studies were identified and characterized. This includes nosylated ureas arising from an alternative cyclization pathway. Finally, post-cleavage oxidation gave access to the Fmoc/Boc-protected alpha-amino acid as well as the corresponding aldehyde. The chiral piperazines described in this work will enable construction of combinatorial libraries with a higher chemical diversity compared to those containing simple N,N'-difunctionalized piperazines, often present in drug-like compounds.

The application of manganese complexes of ligands derived from 1,4,7-triazacyclononane in oxidative catalysis

Since the disclosure that manganese complexes of certain azamacrocyclic ligands were potent low-temperature bleaching catalysts, considerable effort has focussed on their development towards the efficient catalytic oxidation of other substrates, principally with the environmentally benign oxidant H(2)O(2). These efforts have resulted in a broad substrate scope for the system, including alkenes (to give both epoxides and cis-diols as potential products), alcohols, sulfides and C-H oxidation. Additional developments include the heterogenisation of catalytic systems as well as the first generation of enantiomerically pure ligand systems for application in asymmetric epoxidation catalysis. To date there has only been modest success in this regard, but as our understanding of the nature of the active oxidant(s) continues to develop it is likely that there will be viable applications for these systems in the near future.

NMR investigation into the dynamic behaviour of a novel C2-symmetric macrocyclic ligand

The variable-temperature (1)H NMR spectra of a tosylated triazacyclononane are reported. The spectra show a dynamic process which is assigned to hindered rotation about the amide-like N--S bonds, and a value for the free energy of activation for the rotations is derived, DeltaG* = 50.2 kJ mol(-1) at 273 K. Steric and electronic factors which influence the barrier are discussed.

Dirhodium(II) tetra(N-(dodecylbenzenesulfonyl)prolinate) catalyzed enantioselective cyclopropenation of alkynes

Dirhodium tetrakis((S)-N-(dodecylbenzenesulfonyl)prolinate) (Rh(2)(S-DOSP)(4)) is an effective chiral catalyst for the enantioselective cyclopropenation of alkynes by methyl aryldiazoacetates. [reaction: see text]

Synthesis and metal complexation properties of Ph-DTPA and Ph-TTHA: novel radionuclide chelating agents for use in nuclear medicine

We wish to report the synthesis and metal complexation properties of new radionuclide chelating agents for use in nuclear medicine. The strategy includes the facile preparation of rigid analogues of DTPA and TTHA possessing an aromatic ring. The aromatic structure used increased the stability of the complexes formed (pre-organization concept) and they are easily functionalised for attaching to any support. The poly(amino)poly(carboxylic) acids, Ph-DTPA (5a) and Ph-TTHA (5b) were obtained in five steps from phenylenediamine as the starting material with overall yields of 42 and 20%, respectively. The key step in this synthetic process is the preparation of tri- and tetra-amino compounds, 3a and 3b, respectively. In order to assess the ability of both ligands to complex with different metals ((111)In, (153)Sm, (90)Y, (177)Lu, (213)Bi, (225)Ac), along with their suitability for use in nuclear medicine, we used a number of complementary tests. We were able to demonstrate the high complexation capacity of Ph-DTPA (5a) with a broad range of radionuclides in a slightly acidic medium. In vitro stability studies show the high stability of Ph-DTPA with (111)In in human serum, a necessary condition for all medical applications. The protonation constant (log K(H)(i)) of Ph-DTPA (5a) was determined by potentiometric methods.

The synthesis of unsymmetrically N-substituted chiral 1,4,7-triazacyclononanes

A number of chiral unsymmetrically N-substituted 1,4,7-triazacyclononane ligands have been prepared by modular methods. The key step in the synthesis centres on the macrocyclisation of three tertiary amide precursors under standard Richman-Atkins conditions which allows for subsequent N-functionalisation.