Total assignment of 13C and 1H spectra of three isomeric triterpenol derivatives by 2D NMR: an investigation of the potential utility of 1H chemical shifts in structural investigations of complex natural products
1986; Elsevier BV; Volume: 42; Issue: 13 Linguagem: Inglês
10.1016/s0040-4020(01)87309-9
ISSN1464-5416
AutoresWilliam F. Reynolds, Stewart McLean, Janusz Popławski, Raúl G. Enríquez, Laura I. Escobar, Ismael León,
Tópico(s)Natural product bioactivities and synthesis
ResumoIt is shown that a recently proposed indirect heteronuclear shift-correlated pulse sequence, XCORFE, can be used to unambiguously assign the 13C spectra of three isomeric (C30H50O) triterpenols: taraxasterol (1a), pseudo-taraxasterol (2) and lupeol (3). This sequence gives excellent resolution combined with sensitivity far in excess of that given by 13C-13C connectivity experiments. Direct heteronuclear shift-correlated spectra are used to totally assign 1H spectra for 1a, 2, 3 and taraxasteryl acetate (1b). 1H chemical shifts are mainly sensitive to local environment and often show values which are characteristic of a particular environment. Knowledge of 1H chemical shifts and splitting patterns also places useful constraints on assignment of 13C chemical shifts for 13C1Hn units. It is strongly recommended that natural products chemists routinely use 2D NMR to assign 1H chemical shifts of complex organic derivatives in order to build up a data bank of 1H spectral data.
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