Naphthalene dianhydride

Naphthalene-1,5-diol, naphthalene-1,6-diol, dibromoethane, triethyl phosphite, trimethylsilyl bromide, naphthalene dianhydride, ethylene diamine and Boc-anhydride were purchased from Sigma-Aldrich, Bengaluru, Karnataka, India. Acetonitrile and DMF were purchased from S. D. Fine Chemicals Limited (SDFCL). Dichloromethane and Methanol (AR grade) were purchased from Finar chemicals, India, and used without further purification. All reactions were maintained under a nitrogen atmosphere with dry solvents that were degassed for 10–15 min with nitrogen gas. Final compounds were purified using silica-gel column chromatography. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker Avance-400 MHz or 500 MHz spectrometer, or a Bruker Advance 100 MHz or 125 MHz spectrometer at 300 °K as stated. Chemical shifts (in ppm) were referenced to TMS (tetramethylsilane) as an internal standard. All measurements were performed in deuterated chloroform (CDCl₃) or deuterated DMSO (as stated).

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.