The thioester surrogate 3,4-diaminobenzoic acid (Dbz) facilitates the efficient synthesis of peptide thioesters by Fmoc chemistry solid phase peptide synthesis and the optional attachment of a solubility tag at the C-terminus. The protection of the partially deactivated ortho-amine of Dbz is necessary to obtain contamination-free peptide synthesis. The reported carbamate protecting groups promote a serious side reaction, benzimidazolinone formation. Herein we introduce the Boc-protected Dbz that prevents the benzimidazolinone formation, leading to clean peptide o-aminoanilides suitable for the total chemical synthesis of proteins.

We report an operationally simple method to facilitate chemical protein synthesis by fully convergent and one‐pot native chemical ligations utilizing the fluorenylmethyloxycarbonyl (Fmoc) moiety as an N‐masking group of the N‐terminal cysteine of the middle peptide thioester segment(s). The Fmoc group is stable to the harsh oxidative conditions frequently used to generate peptide thioesters from peptide hydrazide or o‐aminoanilide. The ready availability of Fmoc‐Cys(Trt)‐OH, which is routinely used in Fmoc solid‐phase peptide synthesis, where the Fmoc group is pre‐installed on cysteine residue, minimizes additional steps required for the temporary protection of the N‐terminal cysteinyl peptides. The Fmoc group is readily removed after ligation by short exposure (<7 min) to 20 % piperidine at pH 11 in aqueous conditions at room temperature. Subsequent native chemical ligation reactions can be performed in presence of piperidine in the same solution at pH 7.

Apical membrane antigen 1 (AMA1) is a surface protein of Plasmodium sp. that plays a crucial role in forming moving junction (MJ) during the invasion of human red blood cells. The obligatory presence of AMA1 in the parasite lifecycle designates this protein as a potential vaccine candidate and an essential target for the development of novel peptide or protein therapeutics. However, due to multiple cysteine residues in the protein sequence, attaining the native fold with correct disulfide linkages during the refolding process after expression in bacteria has remained challenging for years. Although several approaches to obtain the refolded protein from bacterial expression have been reported previously, achieving high yield during refolding and proper functional validation of the expressed protein was lacking. We report here an improved method of refolding to obtain higher quantity of refolded protein. We have also validated the refolded protein's functional activity by evaluating the expressed AMA1 protein binding with a known inhibitory peptide, rhoptry neck protein 2 (RON2), using surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC).

We report an operationally simple method to facilitate chemical protein synthesis by fully convergent and one‐pot native chemical ligations utilizing the fluorenylmethyloxycarbonyl (Fmoc) moiety as an N‐masking group of the N‐terminal cysteine of the middle peptide thioester segment(s). The Fmoc group is stable to the harsh oxidative conditions frequently used to generate peptide thioesters from peptide hydrazide or o‐aminoanilide. The ready availability of Fmoc‐Cys(Trt)‐OH, which is routinely used in Fmoc solid‐phase peptide synthesis, where the Fmoc group is pre‐installed on cysteine residue, minimizes additional steps required for the temporary protection of the N‐terminal cysteinyl peptides. The Fmoc group is readily removed after ligation by short exposure (<7 min) to 20 % piperidine at pH 11 in aqueous conditions at room temperature. Subsequent native chemical ligation reactions can be performed in presence of piperidine in the same solution at pH 7.

Phosphate diesters are well known to form intermolecular H-bonded dimeric structures in their solid-state. Recently, we reported 2,6-(CHPh) 2-4-iPr-phenyl substituted phosphate diester exists as H-bonded monomeric molecular structure along with water dimer in the solid-state. Herein we report 2,6-(CHPh) 2-4-iPr-phenyl substituted phosphate diester forms a monomeric molecular structure in the solid-state upon cocrystallization with dimethylformamide, DMF (Me 2 NCHO). The-CHO group of DMF simultaneously acts as an H-bond acceptor to P-OH and an H-bond donor to P=O moieties. We also used the alcohols, ROH (R = Me, Et, iPr, and tBu), for crystallisation of 2,6-(CHPh) 2-4-iPr-phenyl substituted phosphate diester. In these instances, solvent-incorporated dimeric structures are found in the solid-state. We also report the syntheses and molecular structures of anionic phosphate diesters of 2,6-(CHPh) 2-4-iPr-phenyl substituted phosphate diester possessing various counter cations. Moreover, we also report the syntheses and molecular structures of phosphate diesters based on (-)-menthol, (?)-menthol and (?)/(-)-menthol. These exist as H-bonded dimers in the solid-state.