Esquire 3000 esi spectrometer

General information: Reagents and dry solvents purchased from commercial sources were used without further purification. Anhydrous reactions were carried out under an atmosphere of argon, using oven-dried glassware. Reactions were monitored using thin layer chromatography (TLC) on aluminium plates precoated with silica gel 60 F254 (Merck, Melbourne, Australia). Developed plates were observed under UV light at 254 nm and then visualised after application of a solution of ninhydrin in EtOH (0.2% w/v) and heating. Flash chromatography was performed on silica gel 60 (0.040–0.063 mm) using distilled solvents. ¹H and ¹³C NMR spectra were recorded at 400 and 100 MHz, respectively, on a Bruker Avance 400 MHz spectrometer. Chemical shifts (δ) are reported in parts per million (ppm), relative to the residual solvent peak as internal reference (DMSO: 2.50 (pent) for ¹H, 39.51 (hept) for ¹³C; D₂O: 4.79 (s) for ¹H). 2D COSY and HSQC experiments were run to support assignments. Low resolution mass spectra (LRMS) were recorded in electrospray ionization mode on a Bruker Daltonics Esquire 3000 ESI spectrometer, using positive mode. The protection of the amino acids used for the amide coupling followed typical procedures to that mentioned in the literature [62 (link),63 (link)].

Reagents and dry solvents purchased from commercial sources were used without further purification. Anhydrous reactions were carried out under an atmosphere of argon, using oven-dried glassware. Reactions were monitored using thin-layer chromatography (TLC) on aluminum plates precoated with Silica Gel 60 F254 (E. Merck). Developed plates were observed under UV light at 254 nm and then visualized after application of a solution of H₂SO₄ in EtOH (5% [vol/vol]) and heating. Flash chromatography was performed on Silica Gel 60 (0.040 to 0.063 mm) using distilled solvents. ¹H and ¹³C NMR spectra were recorded at 400 and 100 MHz, respectively, on a Bruker Avance 400-MHz spectrometer. Chemical shifts (δ) are reported in parts per million, relative to the residual solvent peak as internal reference (CDCl₃, 7.26 [s] for ¹H, 77.0 [t] for ¹³C). Low-resolution mass spectra (LRMS) were recorded, in electrospray ionization mode, on a Bruker Daltonics Esquire 3000 ESI spectrometer, using positive ionization mode. The purity of the final product (compound 3) was determined to be >95% by ¹H and ¹³C NMR. The synthetic work followed the procedures reported in the patent describing PBT2 preparation (13 ). The details of synthetic methods used and full characterization data of the final product are reported below.