Complete assignments of the ¹H and ¹³C NMR spectra of six highly functionalized neoclerodane diterpenoids

Abstract

An NMR study of six highly functionalized neoclerodane diterpenes belonging to both A/B cis and trans series is described. In addition to 1D NMR methods, 2D shift-correlated experiments [

Structural determination and complete NMR spectral assignments of a new diterpenoid obtained from triptonide by biotransformation

“…From comparison with the spectrum of 1, 10 the 13 C NMR spectrum of 2 showed two new peaks at υ 70.7 and 81.4 ppm and two peaks had disappeared between 55 and 65 ppm. Further, in DMSO-d 6 , the signals at υ 5.16 and 5.60 ppm disappeared from the 1 H NMR spectrum of 2 after adding a drop of D 2 O. These two facts provided further confirmation of the deduction.…”

“…A 5 mg amount of 2 was dissolved in 0.5 ml of CD 3 OD or DMSO-d 6 and transferred into two 5 mm NMR tubes. 1 H and 13 C NMR spectra (at 500 and 125 MHz, respectively) were measured at room temperature (22°C/295.1 K).…”

Clerodane Diterpenoids from Salvia splendens

“…The most polar of the compounds isolated from the extract of S. splendens ( 5 ) possesses the molecular formula C 21 H 26 O 5 N 2 , and it was supposed that it is an artifact arising from the initial treatment of the plant extract with diazomethane (see above and Experimental Section). The 1 H and 13 C NMR data of 5 corresponding to the C-1, C-2, and C-5−C-20 structural parts were identical (see Experimental Section) to those of 4 (Table ), and the observed differences were consistent with the presence in the former of a pyrazoline part in which the C-3 and C-4 carbons of the latter are involved. , NOE experiments established a β-configuration for the pyrazoline ring of 5 , because irradiation at δ 2.16 (H-3α proton) produced NOEs in the signals of H-1α, H-3‘a, H-3‘b, and H-19b.…”

“…It is of interest that the facile addition of diazomethane to the α,β-unsaturated-γ-lactone of 4 has been reported previously − for salvifarin, another clerodane diterpene isolated from Salvia farinacea Benth. that also possesses an oxygenated function at the C-2 position.…”

Diterpenoids

“…34 Assignments of the 1 H and 13 C NMR spectra of the clerodanes have been reported. 35 The seeds of Hymenaea courbaril have been reinvestigated and the clerodane 24 has been reported. 36 The thrombin inhibitory constituents of Duranta repens include the clerodane 25.…”