Dry dmf

d-glucosamine HCl, TBTU, T3P, dry DMF, tertiary bases, solvents, and amino acids were purchased from Sigma Aldrich. All chemicals were used without any purification. Before amidation, the optical purity of the L and D amino acids (N-Ac-phe and N-Cbz-phe) was confirmed via polarimeter measurements at 25 °C.

Naphthalene dianhydride, L-glutamic acid, D-glutamic acid, glycine, dry DMF, EDC, Et₃N and DIPEA were purchased from Sigma-Aldrich, Bengaluru, Karnataka, India and were used as received. Ethanol (AR grade 99.9%) was purchased from S.D. fine chemicals Limited (SDFCL), India. Robinson-Britton buffer was prepared by using standard protocol (Annali di Chimica, 1974, 64, 409–412). There action solvents were degassed for 10–15 min using nitrogen gas. The reactions were carried out under nitrogen atmosphere. Silica-gel chromatography technique was used to purify the synthesised compounds. ¹H and ¹³C NMR spectroscopy spectra were measured on Bruker Avance-500 MHz and 125 MHz spectrometer at 27 °C. Tetramethylsilane was used as an internal standard. All experiments were performed in deuterated chloroform (CDCl₃), CDCl₃+ deuterated TFA and DMSO-d₆ wherever required. Electron spray ionization method was employed to ionize the samples with a spray voltage. Mass spectrometry measurements were performed using Fourier transform based high resolution mass spectrometry. IR-Spectra were recorded using Thermo Nicolet Nexus 670 spectrometer in the form of non-hygroscopic KBr pellets.