**4.1 NMR methods**

Benzophenanthridine alkaloids are the most popular class of compounds isolated from *Zanthoxylum* genus. Structures of benzophenanthridines were elucidated by <sup>1</sup> H-, 13C-NMR, DEPT, COSY, HSQC, HMBC, NOESY, and ROESY. The absolute configurations of these compounds were also determined by XRAY, and experimental CD as well as calculated CD.

Study on the structures of benzophenanthridine from *Zanthoxylum* genus, we found some following specifics: dioxymethylene group at C-2 and C-3, unsaturated and saturated bond at N/C-6; some substitutions at C-6 such as sesquiterpenes. **Tables 6** and **7** summarized 13C-NMR characteristics of benzophenanthridine as follows:



#### **Table 6.**

*13C-NMR data of benzophenanthridine alkaloids.*

#### **4.2 Circular dichlorism**

Circular dichroism (CD), a spectroscopic technique based on differential absorption of left- and right-handed circularly polarized light, is ideally disposed to analyze molecular structure, composition and interactions of chiral systems. Quantum mechanical calculations based on density functional theory (DFT) and its timedependent formulation theory (TD-DFT) could be used to determine the theoretical chiroptical response of all the possible conformations of complexed-structures;


#### *Alkaloids and Their Pharmacology Effects from* Zanthoxylum *Genus DOI: http://dx.doi.org/10.5772/intechopen.91685*

**Table 7.**

*13C-NMR data of benzophenanthridine alkaloids (continued).*

by comparison with the experimental CD spectra. This approach can lead to the elucidation of possible absolute structure in the absence of X-ray crystallography or NMR data.

Van et al. isolated four new compounds from *Z. nitidum*. Of these compounds **130** and **131** have the same constitution. This suggested the aglycone could be enantiomer. Thus, the absolute configuration at C-11 of **130** and **131** were elucidated by the comparison of its experimental ECD spectra with those calculated spectra. The TD-DFT calculated ECD spectra [47] of a pair of epimers (**130a** and **131a**) are shown in **Figure 7**. The CD spectra of **130** and **131** were found to be similar to **130a** and **131a** indicating the absolute configuration at C-11 as *R* and S, respectively.

Yang et al., isolated five novel dihydrobenzo[*c*]phenanthridine alkaloids, zanthomuurolanine (**40**), *epi*-zanthomuurolanine (**41**), zanthocadinanine A (**42**), zanthocadinanine B (**43**), and *epi*-zanthocadinanine B (**44**) from *Z. nitidum* [33]. The absolute configurations of these compounds were determined by XRAY and also CD spectra.

Zhao et al. isolated a pair of new enantiomeric furoquinoline alkaloids, zanthonitidine A (**77**) from *Z. nitidum.* There is no obvious absorption of electronic circular dichroism indicated that zanthonitidine A was proposed to be a racemate

#### **Figure 7.**

*Experimental CD and calculated ECD spectra of 130 and 131 (calculated spectra are shifted by* �*8 nm). The figure was cited from Van et al [47].*

#### **Figure 8.**

*Two possible stereochemical structures of 77; experimental ECD spectra of (+)-77/(*�*)-77 and calculated ECD spectra of (8*<sup>0</sup> R*, 9*<sup>0</sup> R*)/(8*<sup>0</sup> S*, 9*<sup>0</sup> S*) of 77. The figure was cited from Zhao et al [24].*

*Alkaloids and Their Pharmacology Effects from* Zanthoxylum *Genus DOI: http://dx.doi.org/10.5772/intechopen.91685*

mixture. Thus, they used Chiralpak ID column chromatography to separate the mixtures to obtain the enantiomers, (+) and (-)-zanthonitidine A. The absolute configurations of the enantiomers were then determined by comparing the experimental CD to the calculated ECD using TD-DFT of the Gaussian 9.0. By analyzing ECD spectra at the same theory level, the absolute configurations of (+) and (�) zanthonitidine A were evaluated as (80 *R*,9<sup>0</sup> *R*)-zanthonitidine A and (8<sup>0</sup> *S*,9<sup>0</sup> *S*) zanthonitidine A [24] (**Figure 8**).

Overall, experimental and calculated ECD spectra could play an important role for determine absolute configurations of alkaloids from *Zanthoxylum* species.
