Camphor nitroimine: a key building block in unusual transformations and its applications in the synthesis of bioactive compounds

The development of new drugs requires a lot of time and high financial investments. It involves a research network in which there is the participation of several researchers from different areas. For a new drug to reach the market, thousands of substances must be evaluated. There are several tools for this and the use of suitable building blocks can facilitate the process by allowing a lead compound to have suitable parameters. These compounds are key structures containing special functional groups that also permit adequate synthetic transformations, leading to several structures of interest in a short period of time. In this review, the use of camphor nitroimine as a potential key building block is explored. Derived from camphor, an abundant natural product present in various plant species, this nitroimine has proved to be quite versatile, allowing the access to substances with miscellaneous biological activities, ligands to asymmetric catalysis, asymmetric oxidants, O-N transfer agents and other applications. Its easy conversion to camphecene and other derivatives is described, as well as their applications in medicinal chemistry. Druglikeness analyses were performed on these studied agents as well as on their bioactive derivatives in order to assess their use in the development of potential drugs.

Synthesis and structure-activity relationships of novel camphecene analogues as anti-influenza agents

A chemical library was constructed based on the scaffold of camphecene (2-(E)-((1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene-aminoethanol). The modifications included introduction of mono-and bicyclic heterocyclic moieties in place of the terminal hydroxyl group of camphecene. All compounds were tested for cytotoxicity and anti-viral activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cells. Among 15 tested compounds 11 demonstrated a selectivity index (SI) higher than 10 and IC₅₀ values in the micromolar range. The antiviral activity and toxicity were shown to strongly depend on the nature of the heterocyclic substituent. Compounds 2 and 14 demonstrated the highest virus-inhibiting activity with SIs of 106 and 183, and bearing pyrrolidine and piperidine moieties, correspondingly. Compound 14 was shown to interfere with viral reproduction at early stages of the viral life cycle (0-2 h post-infection). Taken together, our data suggest potential of camphecene derivatives in particular and camphor-based imine derivatives in general as effective anti-influenza compounds.

Development and validation of ultrafast LC-MS/MS method for quantification of anti-influenza agent camphecene in whole rat blood using dried blood spots and its application to pharmacokinetic studies

A fast, selective and sensitive procedure for quantitation of the camphor-based anti-influenza agent camphecene in whole rat blood was developed and validated using dried blood spots and LC-MS/MS. The method was validated according to recommendations of the FDA and EMA in terms of selectivity, linearity, accuracy, precision, recovery, matrix factor, stability, and carry-over. Sample preparation included spotting 20μL of whole blood taken from the tail vein onto the paper, drying and extracting the analyte, followed by evaporation of the solvent and analysis of the residue. HPLC separations were run on a reversed-phase microcolumn; the time of analysis was less than 2min. MS/MS detection was performed on a triple quadrupole mass-spectrometer using multiple reaction monitoring (MRM) mode. Transitions 196.4→122.2/153.3 and 152.2→93.1/107.2 were monitored for camphecene and 2-adamantylamine hydrochloride (internal standard), respectively. The intra- and inter-day precisions and accuracies, matrix factor, carry-over and recovery were within acceptable limits. Despite low extraction recovery (less than 2%), the sensitivity of the method was enough to detect the analyte in the concentration range 50-2500ng/mL. The application of the method was shown in pharmacokinetic studies of camphecene in rats at a dose of 10mg/kg.