assignments of hydrogen and carbon atoms of artemisinin

Assignments of Hydrogen and Carbon Atoms of Artemisinin

Elvis Chua

Artemisinin is a sesquiterpene lactone.

•Molecular formula: C15H22O5

•Has been studied to be a cure for malaria

1 23

45

6

7 8

9

10

1H NMR NON spectrum shows 10 distinct hydrogen peaks.

It is expected that there are overlapping peaks because artemisinin has 12 different types of hydrogen atoms.

Some of the hydrogen atoms can be assigned to their corresponding peaks.

An additional proton peak was assigned using the COSY spectrum.

H5 is assigned to Peak 6.

13C NMR BCM spectrum shows the 15 carbon peaks.

AB

C

D

E F G H I JK

L

NMO

CDCl3

The quaternary carbon atoms are assigned by comparing the spectra from the BCM and DEPT45 experiments.

Only one secondary carbon is assigned by comparing BCM and DEPT135 spectra.

The primary carbon atoms are assigned by comparing BCM and DEPT90 spectra.

The tertiary carbon peaks are not much affected in DEPT 90.

The HMQC spectrum confirmed most of the initial assignments.

• Quaternary carbon atoms have no correlations.

• C7-H7 correlation is observed.

The HMQC spectrum confirmed most of the initial assignments.

• Some other correlations observed:• C13-H13• C14-H14• C15-H15

The HMQC spectrum also gave new 13C assignments.

• C11 is assigned to Peak J.

H11

Peak G can now be assigned to C2.

E F GC J

DEPT90 spectrum

Because it is the less deshielded among the three remaining tertiary carbon atoms

HMBC spectrum completed the tertiary carbon atom assignments.

Carbon Peak HMBC Correlations

E

4 (2.035ppm)6 (1.778ppm)7 (1.437ppm)

H14

F

2 (3.392ppm)5 (1.976ppm)6 (1.778ppm)8 (1.209ppm)9 (1.082ppm)

C1 is closer to H14 than C5. C1Peak EC5Peak F

HMBC spectrum also completed the secondary carbon atom assignments.

Carbon PeakHMBC

CorrelationsI H14L H9e

M6 (1.778ppm)9 (1.082ppm)

C3 is the closest to H14. C10 is the closest to H9e.

C3Peak IC10Peak LC4Peak M

• Each secondary carbon atom peak had correlations with two proton peaks.

The HMQC spectrum showed that the protons attached to secondary carbon atoms are not

equivalent.

Axial and equatorial protons can easily be assigned to their corresponding peaks.

• Because equatorial protons are more deshielded than axial protons.

• Where is 10a?

9e 9a 3e 3a4e 4a

10e

10a could be part of Peak 7.From NON, integration of Peak 7 is 6.20.

3H’s1H1H-----5H’s only

CONCLUSION

• Complete assignment of proton and carbon peaks were done using different NMR techniques.

• The following tables show a summary of the assignments.

Proton Assignments

Label ppm Multiplicity J (Hz) Assignments1 5.866 s - H7

2 3.392 dq 7.205.19 H11

3 2.429 m - H9e4 2.035 m - H9a, H10e5 1.976 m - H4e6 1.778 m - H3e, H5

7 1.437 m - H15, H2, H1, H10a

8 1.209 d 7.49 H139 1.082 m - H3a, H4a

10 1.005 d 6.00 H14

Carbon Assignments

Carbon peak label ppm(bcm)

Assignment / Comments

A 172.275 C12B 105.493 C8C 93.820 C7D 79.594 C6E 50.109 C1F 44.987 C5G 37.555 C2H 35.929 C9I 33.634 C3J 32.920 C11K 25.229 C15L 24.865 C10M 23.241 C4N 19.849 C14O 12.569 C13

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