Total 1H NMR assignment of 3β-acetoxypregna-5,16-dien-20-one

•The total assignment of the 1H NMR of 3β-acetoxypregna-5,16-dien-20-one is described.•Assignments were made extracting JHH values from a HSQC, and using PERCH software.•Experimental 3JHH vs. values calculated by Altona give excellent correlations.•Comparison applied to testosterone suggested the reassignment of four 3JHH data.

This work describes the total and unambiguous assignment of the 750 MHz 1H NMR spectrum of 3β-acetoxypregna-5,16-dien-20-one or 16-DPA (1), the well-known intermediate utilized in the synthesis of biological important commercial steroids. The task was accomplished by extracting the coupling constant values in the overlapped spectrum region by HSQC, and using these values in the 1H iterative full spin analysis integrated in the PERCH NMR software. Comparison of the experimental vicinal coupling constants of 1 with the values calculated using Altona provides an excellent correlation. The same procedure, when applied to the published data of progesterone (2) and testosterone (3), afforded an acceptable correlation for 2 and a poor correlation for 3. In the last case, this suggested the reassignment of all four vicinal coupling constants for the methylene signals at the C-15 and C-16 positions, demonstrating the utility of this methodology.

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