{'fraction_non_alphanumeric': 0.08105022831050228, 'fraction_numerical': 0.03424657534246575, 'mean_word_length': 4.621794871794871, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Application of NMR spectroscopy for assignment of the absolute configuration of 8-tert-butyl-2-hydroxy-7-methoxy-8-methyl-9-oxa-6-azaspiro[4.5]dec-6-en-10-one.

In order to assign the absolute configurations of 8-tert-butyl-2-hydroxy-7-methoxy-8-methyl-9-oxa-6-azaspiro[4.5]dec-6-en-10-one (2a,b), their esters (5a-d) with (R)- or (S)-2-methoxyphenylacetic acid (4a,b) have been synthesized. The absolute configurations of these compounds have been determined on the basis of NOESY correlations between the protons of the tert-butyl group and the cyclopentane fragment of the molecules. The crucial part of this analysis was assignment of the absolute configuration at C-5. Additionally, by calculation of the chemical shift anisotropy, δ(RS), for the relevant protons, it was also possible to confirm the absolute configurations at the C-2 centres of compounds 2a,b and 5a-d.