Cptci micro cryoprobe

Based on the simulated shielding tensors, NMR chemical shifts were simulated by comparison with published data of the respective compounds: 20-hydroxy-13,19-didesmethyl SPX C [14 (link)] (Supplementary Materials Table S1), and 20-hydroxy-13,19-didesmethyl SPX D [14 (link)] (Table S1); 13-desmethyl SPX C [23 (link)] (Table S1); 13,19-didesmethyl SPX C [8 (link)] (Table S1); 7,6-spirocyclic imine [10 (link)] (Table S2), GYM A [21 (link),22 (link)] (Table S2 “C-4: S; NP”); C-4 R epimer of GYM A [13 (link)] (Table S2 “C-4: R; syn”); 12-methyl GYM B [24 (link)] (Table S2), 16-desmethyl GYM D [14 (link)] (Table S2). The ROESY spectra of 20-hydroxy-13,19-didesmethyl SPX C in MeOD were recorded in 1.7 mm microtubes at 292 K with an AVANCE II 600 MHz NMR spectrometer (Bruker) and a CPTCI micro-cryoprobe.

Purified compounds were dried under vacuo and taken up in 45 µL deuterated pyridine (Pyr-d₅) containing 0.03% TMS (compounds GYM A, 1, 2 and 10) or 45 µL deuterated methanol (MeOD; SPX STD, 10 and 11). NMR experiments were performed in 1.7 mm microtubes at 292 K with a AVANCE II 600 MHz NMR spectrometer (BRUKER) and a CPTCI microcryoprobe. Chemical shift referencing was performed against TMS. BRUKER standard pulse programs were used except for heteronuclear multiple bond correlation (IMPACT-HMBC) [26 (link)].