Complete NMR Assignment of MogrosidesII A2, II E andIII A1Isolated from Luo Han Guo

Complete NMR Assignment of MogrosidesII…
Table 2. 1 H and 13 C NMR (500 and 125 MHz, CD 3 OD), assignments forthe glycosides of 1, 2, and 3.
1 2 3
Position
13 C
1 H
13 C
1 H
13 C
1 H
Glc I -1 --- --- 104.9 4.33 d (7.7) 104.2 4.43 d (7.3)
Glc I -2 --- --- 75.3 3.21 m 81.2 3.61 m
Glc I -3 --- --- 78.0 or 78.1 3.35 m 78.7 3.59 m
or 78.3
Glc I -4 --- --- 71.6 or 71.7 3.28 m 71.6 3.33 m
Glc I -5 --- --- 78.0 or 78.1 3.27 m 76.5 3.50 m
or 78.3
Glc I -6 --- --- 62.6 3.64 m
3.84 m
70.1 3.62 m
4.23 dd
(10.4, 1.8)
Glc II -1 --- --- --- --- 104.4 or 104.5 4.28 d (7.7)
Glc II -2 --- --- --- --- 75.2 3.20 m
Glc II -3 --- --- --- --- 77.7-78.2 ¥ 3.36 m
Glc II -4 --- --- --- --- 71.6 3.27 m
Glc II -5 --- --- --- --- 77.7-78.2 ¥ 3.26 m
Glc II -6 --- --- --- --- 62.7 3.65 m
3.85 m
Glc III -1 --- --- --- --- 104.4 or 104.5 4.77 d (7.8)
Glc III -2 --- --- --- --- 75.7 3.27 m
Glc III -3 --- --- --- --- 77.7-78.2 ¥ 3.36 m
Glc III -4 --- --- --- --- 72.4 3.21 m
Glc III -5 --- --- --- --- 77.7-78.2 ¥ 3.27 m
Glc III -6 --- --- --- --- 63.6 3.63 m
3.86 m
Glc IV -1 106.4 4.28 d (7.8) 106.6 4.27 d (7.8) --- ---
Glc IV -2 75.2 or 75.6 3.19 m 75.6 3.18 m --- ---
Glc IV -3 78.1 3.31 m 78.0 or 78.1 3.31 m --- ---
or 78.3
Glc IV -4 71.6 3.29 m 71.6 or 71.7 3.26 m --- ---
Glc IV -5 77.2 3.40 m 77.7 3.21 m --- ---
Glc IV -6 69.8 3.80 m
4.05 dd
62.8 3.65 m
3.81 m
--- ---
(11.8, 1.5)
Glc V -1 104.8 4.42 d (7.8) --- --- --- ---
Glc V -2 75.2 or 75.6 3.18 m --- --- --- ---
Glc V -3 77.9 or 78.0 3.35 m --- --- --- ---
Glc V -4 71.6 3.28 m --- --- --- ---
Glc V -5 77.9 or 78.0 3.25 m --- --- --- ---
Glc V -6 62.7 3.66 m --- --- --- ---
3.85 m
¥ Four carbon resonances in the range of 77.7-78.2 (77.66, 77.92, 77.05, and 78.16), hence chemical shifts could not be unequivocally assigned.
The 1 H and 1 H- 13 C HSQC-DEPT data allowed identification of the two anomeric protons inMogroside II A 2
which were well resolved at H 4.42 ( C 104.8) and 4.28 ( C 106.4) and both protons had large couplings (7.8
Hz) indicating that they had β-configurations. The anomeric proton at H 4.28 showed an HMBC correlation to
C-3 ( C 88.2)which indicated that it corresponded to Glc IV H-1.Glc IV H-2 and H-3 were then assigned based on
COSY correlation between Glc IV H-1/Glc IV H-2 and Glc IV H-2/Glc IV H-3.Due to data overlap the COSY
spectrum did not allow assignment of remaining Glc IV protons. Therefore, 1D TOCSY experiments were
performed to assignGlc IV H-4, H-5 and H-6. HSQC-DEPT data was then used to assign the carbon chemical
shift of Glc IV C-1 to C-6.HMBC correlations ofGlc IV H-1/C-2, C-3, C-5; H-2/C-1; H-3/C-2, C-4;H-4/C-6 and H-
6/C-4 further confirmed the assignments.The complete 1 H and 13 C assignments forGlc IV are presented in Table 2.
The downfield carbon chemical shift of C-6 (δ C 69.8) indicated that the hydroxyl group at C-6 is replaced by a
sugar linkage.The anomeric proton of Glc V at H 4.42 showed an HMBC correlation to the carbon at C 69.8
ppm (Glc IV C-6) and the reciprocal HMBC correlations from the methylene protons of Glc IV ( H 3.80 and 4.05)
to the anomeric carbon ofGlc V at C 104.8 confirmedthe 16 linkage between Glc V and Glc IV .The remaining
proton and carbon assignments for Glc V wasdone as discussed above for Glc IV . The key 1 H- 1 H COSY and 1 H- 13 C
HMBCcorrelations for theglycone unit of Mogroside II A 2 (1) are presented in Figure 2 (B) and the complete
proton and carbon assignments are presented in Table 2.
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