Improved Synthesis of D‐Isoglutamine: Rapid Access to Desmuramyl Analogues of Muramyl Dipeptide for the Activation of Intracellular NOD2 Receptor and Vaccine Adjuvant Applications

Abstract

Muramyl dipeptide (MDP) -the smallest immunomodulatory unit of bacterial peptidoglycan -has adjuvant activity and triggers the innate immune system against bacterial and viral infections. The inherited drawbacks of MDP, such as pyrogenicity and poor macrophage penetration, can be resolved by structural modifications, thereby improving its pharmacological profile and adjuvant activity. Herein, several desmuramyl analogues of MDP were designed by replacing the carbohydrate fragment (MurNAc) of the parent molecule with an immunomodulatory xanthine scaffold. The LÀ D configurations of the pharmacophoric dipeptidyl moiety were conserved and alkyl chains of moderate length were introduced at isoglutamine to enhance their cellular uptake. The synthesis of these analogues features a novel synthetic route for D-isoglutamine fragment with an overall yield of > 50 % in ten to eleven steps. This sufficiently flexible approach provides rapid access to desmuramyl analogues of MDP on a gram scale, which can help accelerate the development of novel NOD2 agonists and immunoadjuvants.

Synthesis and Immunological Evaluation of Mannosylated Desmuramyl Dipeptides Modified by Lipophilic Triazole Substituents

“…Several SAR studies of NOD2 agonists have been reported, including synthetic modifications at the saccharide and peptide parts of MDP [ 7 , 8 , 19 , 20 , 21 ]. Carbohydrate moiety (muramic acid) can be replaced by different substituents [ 6 ] and increase of lipophilicity can lead to improved immunostimulating activity [ 7 , 8 , 9 , 22 ]. Mifamurtide (liposomal muramyl tripeptide phosphatidyl ethanolamine) is a synthetically modified MDP and a clinically used therapeutic agent [ 23 ].…”

“…In mifamurtide, phospholipids facilitate the incorporation of the peptide part into liposomes due to the lipophilicity. Therefore, the introduction of lipophilic substituents has been the mainstream of SAR studies [ 6 ]. Our research is focused on the preparation of MDP mimetics, primarily modified by lipophilic adamantane due to the fact that adamantane DMPs are devoid of the undesirable side-effect [ 6 ].…”

“…Therefore, the introduction of lipophilic substituents has been the mainstream of SAR studies [ 6 ]. Our research is focused on the preparation of MDP mimetics, primarily modified by lipophilic adamantane due to the fact that adamantane DMPs are devoid of the undesirable side-effect [ 6 ]. Additionally, bulky adamantane can act as a membrane anchor and can be used for the preparation of liposomes and other similar drug delivery systems [ 24 , 25 , 26 , 27 ].…”

“…Herein, we have explored the influence of three lipophilic triazole-containing substituents (adamantyl, adamantylethyl and C 12 alkyl) on the activity of mannosylated DMP. Bulky adamantane was selected due to its beneficial properties as well as its lipophilicity and alkyl chain because clinically important MDP derivatives (murabutide, mifamurtide, B 30 -MDP) are modified by alkyl chains of moderate length [ 6 ]. The partition coefficient between n -octanol and water, called the log p value, is a classical descriptor of lipophilicity and can be predicted using computational methods.…”

“…Structure-activity relationship studies showed that carbohydrate moiety (muramic acid in MDP) is not essential for immunomodulation [ 6 ] and it can be replaced. MDP analogues lacking the N -acetylmuramyl group are called desmuramyl peptides (DMPs).…”