A new paradigm for designing ring construction strategies for green organic synthesis: implications for the discovery of multicomponent reactions to build molecules containing a single ring

A new way of developing novel synthesis strategies for the construction of monocyclic rings found in organic molecules is presented. The method is based on the visual application of integer partitioning to chemical structures. Two problems are addressed: (1) the determination of the total number of possible ways to construct a given ring by 2-, 3-, and 4-component couplings; and (2) the systematic enumeration of those possibilities. The results of the method are illustrated using cyclohexanone, pyrazole, and the Biginelli adduct as target ring systems with a view to discover new and greener strategies for their construction using multicomponent reactions. The application of the method is also extended to various heterocycles found in many natural products and pharmaceuticals.

Applications of C-H functionalization logic to cyclobutane synthesis

The application of C-H functionalization logic to target-oriented synthesis provides an exciting new venue for the development of new and useful strategies in organic chemistry. In this article, C-H functionalization reactions are explored as an alternative approach to access pseudodimeric cyclobutane natural products, such as the dictazole and the piperarborenine families. The use of these strategies in a variety of complex settings highlights the subtle geometric, steric, and electronic effects at play in the auxiliary guided C-H functionalization of cyclobutanes.

Investigations into the synthesis, radiofluorination and conjugation of a new [¹⁸F]fluorocyclobutyl prosthetic group and its in vitro stability using a tyrosine model system

The [(18)F]fluorocyclobutyl group has the potential to be a metabolically stable prosthetic group for PET tracers. The synthesis of the radiolabeling precursor cis-cyclobutane-1,3-diyl bis(toluene-4-sulfonate) 8 was obtained from epibromohydrin in 7 steps (2% overall yield). The radiolabeling of this precursor 8 and its conjugation to L-tyrosine as a model system was successfully achieved to give the new non-natural amino acid 3-[(18)F]fluorocyclobutyl-L-tyrosine (L-3-[(18)F]FCBT) [(18)F]17 in 8% decay-corrected yield from the non-carrier-added [(18)F]fluoride. L-3-[(18)F]FCBT was investigated in vitro in different cancer cell lines to determine the uptake and stability. The tracer [(18)F]17 showed a time dependent uptake into different tumor cell lines (A549, NCI-H460, DU145) with the best uptake of 5.8% injected dose per 5×10(5) cells after 30min in human lung carcinoma cells A549. The stability of L-3-[(18)F]FCBT in human and rat plasma and the stability of the non-radioactive L-3-FCBT in rat hepatocytes were both found to be excellent. These results show that the non-natural amino acid L-3-[(18)F]FCBT is a promising metabolically stable radiotracer for positron emission tomography.

Carbonylation of 1-lithiobutadiene with carbon monoxide followed by intramolecular acyllithiation of C═C double bond and intermolecular acylation with acid chloride: scope, applications, and mechanistic aspects

The carbonylation of a 1-lithio-1,3-butadiene derivative with CO gave rise to a butadienyl acyllithio intermediate, which underwent an immediate intramolecular acyllithiation of the C═C double bond, affording a lithio cyclopentadienyl enolate. The X-ray structural analysis of the enolate revealed a dimer connected with a "Li(2)O(2)" four-membered ring. Subsequent intermolecular acylation of this enolate with acid chlorides afforded β-keto-3-cyclopentenones, γ-keto-2-cyclopentenones, or cyclopentadienyl ester derivatives. The stereo- and regioselectivity of the in situ generated lithio cyclopentadienyl enolate with various acid chlorides was investigated and analyzed, showing that the formation of the above products was significantly dependent on both the substituents on the butadienyl skeleton and the bulkiness of acid chlorides.

Improved synthesis of anti-[18F]FACBC: improved preparation of labeling precursor and automated radiosynthesis

The non-natural amino acid anti-1-amino-3-[18F]fluorocyclobutyl-1-carboxylic acid (FACBC) has shown promise for tumor imaging with positron emission tomography. An improved synthesis of the precursor of anti-[18F]FACBC has been devised which demonstrates high stereoselectivity and suitability for large-scale preparations. An automated radiosynthesis has been developed which provides anti-[18F]FACBC in 24% decay-corrected yield. Additionally, the major non-radioactive species present in doses of anti-[18F]FACBC has been identified as anti-1-amino-3-hydroxycyclobutane-1-carboxylic acid. Together, these results are important steps towards the routine production of anti-[18F]FACBC for human use.

Design and synthesis of inhibitors of inducible nitric oxide synthase. Discovery of a new chemical lead with potential for oral bioavailability

A series of 2-iminopiperidines fused to small-membered rings (Tables 1 and 2) were synthesised and biologically evaluated using an in vitro human nitric oxide synthase (NOS) inhibition assay. Fused bicyclic compounds 5-9 exhibited nearly the same potency as compound 1 in the hiNOS inhibition assay. Among these, the 1-methyl analogues 8 and 9 showed better isoform selectivity than their corresponding unsubstituted analogues 7 and 6, respectively. Compounds 5 and 6 were also evaluated by an in vivo NO accumulation assay in a mouse model. The discovery process of new chemical leads for an orally bioavailable inhibitor of human inducible NOS (iNOS) is reported. The structure-activity relationship (SAR) study and chemistry of these compounds are also reported.