Fmoc solid-phase synthesis of RF9 optimization with mass spectrometry verification

The RF9 compound, which is an antagonist of the FF neuropeptide receptors is used as a therapeutic substance to improve the effectiveness of opioids in the chronic treatment of pain. The purpose of this study was to find the most efficient method of RF9 synthesis. The optimization experiment involved solid-phase peptide synthesis. The Fmoc strategy is based on the usage of the 9-fluorenylmethoxycarbonyl group to block reactive amino groups. Commonly applied RF9 synthesis is based on DIC/HOBt activation of 1-adamantanecarboxylic acid prior to its substitution. The experiments carried out in this research were based on the routinely applied DIC/HOBt carboxylic group activation and this scheme was compared with the COMU/DIPEA and DIC approach. The obtained results showed that COMU/DIPEA was the most efficient and effective method of RF9 synthesis. Using this strategy, pure compound was obtained, without any by-products, and at a highest yield. The use of COMU/DIPEA can be an excellent alternative to the routinely used RF9 synthesis.