Resonance gauche-trans shift

The D loop resonance is downshifted, which indicates a shift away from a gauche, gauche phosphoester configuration toward a gauche, trans. 

The P-configuration assigned to this tertiary hydroxyl group in teupestalin A (108) was supported by the very deshielded resonance of one of the C-11 methylene protons [H-1 la (pro-S), 8 3.47 dd, J= 1.5 and 3.7 Hz] which is close to the lOP-hydroxyl group, and by comparison of the NMR spectral data of 113 and 114 (Table 13). Since the observed differences in the chemical shifts of the C-8 [A8 = 8(1)- 8(3), -6.2 ppm] and C-11 (A8-7.7) y-carbons were only compatible with a y-gauche arrangement [66], whereas for a 10a-hydroxyl substituents, smaller shielding effects are expected on these carbon atoms, at least on C-11 (y-trans carbon) [67]. 

The chemical shift between the resonance maxima in PE presumably arises from constraint to trans bond conformations in the crystalline region as opposed to trans/gauche conformations in the amorphous regions. Assuming the chemical shift difference (6.4 ppm) between the crystalline peak in PE and the resonance of cyclohexane which exists in an all gauche conformation can be attributed entirely to conformational effects, Earl and VanderHart have concluded that the 2.3 ppm shift between resonances for the crystalline and... 

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