Synthesis And Antifungal Activity Of The Glycopeptide Compounds

Nowadays, it is still urgent to develop new type antifungal drugs with broad spectrum, high efficiency and low toxicity for the increasing growth of deep fungal infections in clinic. Cyclopeptides are a kind of compounds pocessing various bioactivities such as antibacterial, antitumor, antivirus and so on. Echinocandins are a class of fungicidal cell-wall active lipopeptides. These compounds can interfere the synthesis of β-1,3-D-glucan, the main component of fungal cell wall, through inhibiting β-1,3-D-glucan synthase in fungal cell membranes, resulting in the cell wall’s discruption of fungi, and eventually leading to the fungi cleavage to death. Echinocandins, inlcuding caspofungin, micafungin and anidulafungin, have been widely used in clinic due to their excellent antifungal activity, low toxicity, and not easy to generate scarce drug resistance.Carbohydrate, the vital component of organism, mainly exists on the cell surface in form of glycoproteins and glycolipids. It is not only the important source of energy and carbon, but also plays key roles in the aspects of cell adhesion, phagotrophy and signal transmission. In addition, carbohydrate is a molecule with multi functional groups. Meanwhile, many of the natural cyclic peptides were glycosylated, and the glycans usually play a pivotal role in their biological functions, as well as their other properties such as stability, aqueous solubility, conformational stability and target binding affinity. Caspofungin is a lipophilic peptide that has poor aqueous solubility, thus it is usually used in the diacetate form (Cancidas(?)), which is highly hygroscopic and prone to produce allergic reaction and neurotoxicity discovered in the clinical use. Based on the previous researches, we can assume that introducing glycosyl to the structure of caspofungin may improve its antifungal activity, water solubility, stability and alleviate its adverse effects.In the present study, six glycosylated derivatives of caspofungin2a-f have been designed and synthesized. The target compounds were obtained via substitution, reduction, amidation, esterfication, condensation with caspofungin and two-steps deprotection from the starting material of the commercially available peracetylated β-D-glucopyranose,β-D-glalactopyranose,β-D-xylopyranose, α-L-rhamnopyranose, β-maltose and β-lactose. All of them were first reported and their structures were confirmed by’H-NMR,13C-NMR and HR-QTOF-MS.The antifungal activities of2a-f were evaluated with seven fungal strains purchased from American Type Culture Collection (ATCC), including Candida albican (C. albican) Y0109, C. albican SC5314, C. parapsilosis22019, C. krusei537, Cryptococcus neoformans (C. neoformans)32609, Microsporum gypseum (M. gypseum) Cmccfmza, and Trichophyton rubrum (T. rubrum) Cmccftla. Their minimum inhibition concentrations (MICs) against the fungi were determined according to the method recommen-ded by the National Committee for Clinical Laboratory Standards (NCCLS). The preliminary test results showed that:all the compounds had certain antifungal activity. Compounds2a-d, containing monosaccharides in their structures, showed better antifungal activities than the compounds2e-f containing disaccharides in their structure. In particular, compound2a had significantly better antifungal activities than caspofungin against all of the tested fungal strains but C. albican SC5314. In addition, its water solubility and stability were also significantly superior to caspofungin. In summary, this study has great significance for the action mechanism research of echinocandins and the development of the new type antifungal drugs. Nowadays, modification of bioactive natural lead compounds has been an important and convenient way for developing new drugs. Tunicyclin D, a cyclooctapeptide with potent antifungal activity, was separated from the roots of Psammosilene tunicoides by the group of professor Zhang who has been working in our pharmaceutical school. Recently, our group has successfully developed several new synthetic routes for preparing novel glycocyclicpeptides. In the present study, Tunicyclin D was firstly synthesized by solid phase strategy. Meanwhile, seven glycosylated derivatives were designed and synthesized to investigate-the impact of different glycosyls on its antifungal activities and further explore their structure and activity relationship.In the total synthesis, the commercially available glucopyra, maltose and lactose were used as the starting material, and the key intermediates of full acetyl protected glycosyl amino acids5a-g were obtained after several steps and used in the solid phase synthesis. Totally we got seven fully protected liner glycosyl octapeptides6a-g via amidation and depeotection, and the cyclization was done in liquid phase with good yield. After two steps deprotection, seven new Tunicyclin D glycosyl derivatives were obtained. All of the target compounds were reported firstly and their structure were confirmed by1H-NMR,13C-NMR and HR-QTOF-MS.The antifungal activities of la-g and Tunicyclin D were evaluated with five fungal strains purchased from American Type Culture Collection (ATCC), including Candida albican (C. albican) Y0109, C. albican SC5314, C. parapsilosis22019, Trichophyton rubrum (T. rubrum) Cmccftla and Trichophyton mentagrophytes (T. mentagrophytes)0236. Their minimum inhibition concentrations (MICs) against the fungi were determined according to the method recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The preliminary pharmacological results showed that all the target compounds have maintained the antifungal activity of Tunicyclin D, and some of them had better antifungal activity against some fungi than the synthesized Tunicyclin D. Compound1f was indentified as most potent compound. In summary, this study has great significance for development of new type of antifungal drugs.