Study On Synthesis And Biological Activity Of Several Diketopiperazines

As aquaculture activities of our country intensify and expand, the disease problems caused by viruses, bacteria, parasites and other undiagnosed and emerging pathogens has become a primary constraint to the culture of many aquatic species. Traditionally, antibiotics have been generally adopted to treat diseases of aquatic animals. But these are no longer recommended practices due to the accumulation of drugs in tissues, development of drug resistance and enviromental pollution. Immunostimulants can improve the immune system of animals body and also enhance the ability to prevent diseases. The resorce of the immunostimulants includs aimal, plant and microorganisms. At present as the discovery of bioactive compounds from secondary metabolites of microorganisms, it is feasible to develop new immunostimulants aquaculture which leaded by the active compound from microorganisms. In the previous study, cyclo-(L-Pro-Gly) which come from the secondary metabolites of Anoxybacillus kamchatkensis XA-1 was determined to have the immunostimulatory activities to carp. So, in the present study, we synthesis the several diketopiperazines with the raw material of L-Pro, Gly, L-Phe et al. and evaluate their immunostimulatory activities on CIK cells to develop potential medicines for the control of fish disease.In this work, six diketopiperazines (cyclo-(L-Pro-Gly), cyclo-(Gly-Gly), cyclo-(L-Val-Gly), cyclo-(L-Ala-Gly), cyclo-(L-Phe-Gly) and cyclo-(L-Pro-L-Pro)) were synthesis through the solid-phase synthesis by the protection of amino group (Fmoc), the protection of carboxy (methyl esterification), condensation with Wang resin, deprotection of of amino group, condensation with amino acid, elution off the resin and cyclization with the raw material of L-Pro, Gly, L-Val, L-Ala and L-Phe. All the compounds were identified by 1H NMR and 13C NMR.At tha same time, six diketopiperazines (cyclo-(L-Phe-L-Val), cyclo-(L-Val-L-Leu), cyclo-(L-Pro-L-Pro), cyclo-(L-Phe-L-Ala), cyclo-(L-Phe-L-Phe), cyclo-(L-Phe-L-Leu) through the liquid-phase synthesis by the protection of amino group (Fmoc), the protection of carboxy (methyl esterification), condensation with amino acid, deprotection of of amino group and cyclization in methanol with the raw material of L-Pro, L-Val, L-Ala, L-Leu and L-Phe. All the compounds were identified by 1H NMR and 13C NMR.Real-time qPCR indicated that the potential receptor inside the cell of diketopiperazines represented by cyclo-(L-Pro-Gly) is Toll-like receptor 4 and identify a signaling pathway by which the body can express the cytokines in the downstream to improve the non-specific immune system and it also reflected that diketopiperazines can produce the immunostimulatory activities.