Synthesis of Bioactive Complex Small Molecule-Ciprofloxacin Conjugates and Evaluation of Their Antibacterial Activity.

Conjugates between pharmaceuticals and small molecules enable access to a vast chemical space required for the discovery of new lead molecules with modified therapeutic potential. However, the dearth of specific chemical reactions that are capable of functionalizing drugs and bioactive natural products presents a formidable challenge for preparing their conjugates. Here, we report a support-free CuI-nanoparticle-catalyzed strategy for conjugating electron-deficient and electron-rich terminal alkynes with a ciprofloxacin methyl ester. Our conjugation technique exploits the late-stage functionalization of bioactive natural products such as tocopherol, vasicinone, amino acids, and pharmaceuticals such as aspirin and paracetamol to provide conjugates in excellent yields under mild and green conditions. This protocol also enabled the synthesis of (hetero)arene-ciprofloxacin 1,4-disubstituted 1,2,3-triazoles in good yields and high regioselectivities. These synthesized ciprofloxacin conjugates were evaluated in vitro for their antibacterial activity against a panel of relevant bacteria. A significant number of conjugates showed comparable activity against Gram-positive and Gram-negative bacteria. Moreover, some conjugates exhibited less toxicity than ciprofloxacin against two mammalian cell lines, suggesting the utility for the future investigation of these compounds for in vivo efficacy and pharmacokinetic studies.

2-Aminoquinazolin-4(3H)-one as an Organocatalyst for the Synthesis of Tertiary Amines.

The potential of 2-aminoquinazolin-4(3H)-one as an organocatalyst for the activation of aldehydes via noncovalent interaction for the synthesis of tertiary amines using formic acid as a reducing agent is reported for the first time. The developed protocol demonstrated a dilated substrate scope for aromatic and aliphatic amines with aromatic and aliphatic aldehydes. Furthermore, the current method was also fruitful for the derivatization of ciprofloxacin and its derivative in good to excellent yields.

Microwave assisted synthesis of phenanthridinones and dihydrophenanthridines by vasicine/KOtBu promoted intramolecular C-H arylation.

A simple, efficient, rapid and transition metal-free methodology has been developed by utilizing vasicine (a natural product), as a catalyst for the synthesis of phenanthridinones and dihydrophenanthridines. The reaction proceeds through intramolecular C-H arylation with aryl halides in the presence of KOtBu as a base under microwave irradiation in sulfolane as a solvent. The reaction proceeds well with various aryl iodides, bromides and more remarkably with less reactive aryl chlorides for 15 minutes, providing the corresponding products in 45-90% yields.

Synthesis of tertiary arylamines: Lewis acid-catalyzed direct reductive N-alkylation of secondary amines with ketones through an alternative pathway.

We report herein a highly efficient, tin(ii)/PMHS catalyzed reductive N-alkylation of arylamines with ketones affording tertiary arylamines. A very wide substrate scope was observed for the current catalytic method as all six permutations of ketones/aldehydes/heterocyclic carbonyls and primary/secondary/heterocyclic amines were well tolerated, enabling access to secondary, tertiary and heterocyclic amines. The method is also convenient for the synthesis of N-substituted isoindolinones and phthalazinones via a tandem amination-amidation sequence. Mechanistic investigations revealed a carbocationic pathway instead of an ordinary direct reductive amination pathway.

Chemoselective Reductive Amination of Carbonyl Compounds for the Synthesis of Tertiary Amines Using SnCl2·2H2O/PMHS/MeOH.

Stannous chloride catalyzed chemoselective reductive amination of a variety of carbonyl compounds with aromatic amines has been developed for the synthesis of a diverse range of tertiary amines using inexpensive polymethylhydrosiloxane as reducing agent in methanol. The present method is also applicable for the synthesis of secondary amines including heterocyclic ones.