Chemical Constituents of Cannabis

Many of the chemical constituents of Cannabis are common to other plants; however, cannabinoids are unique to their namesake (33). Of the hundreds of chemicals found in Cannabis—and described at length in this book—175 were used to develop the chemical fingerprint system. Of those compounds readily detectable by the methods developed in phase I, 46 were positively identified, including 22 monoterpenes or sesquiterpenes, 16 cannabinoids, two noncannabinoid phenols, two hydrocarbons, three fatty acid esters, and one miscellaneous aromatic compound (see Table 1). The remaining 129 compounds were necessarily included because all of the chemical compounds contribute to the fingerprint, and only the multivariate data analysis software could sort out which ones were important to establish relationships and differentiate between the classes.

For the fingerprint system to be of practical use in all laboratories, the methods needed to be reproducible and cost-effective, so simple methods using common laboratory equipment were developed. The methods used in this study have not been validated for reproducibility between different laboratories, but because of the simple analytical techniques employed we assumed that the methods would be robust and that different laboratories could generate similar data in house. Because the fingerprint chromatograms are so complex, however, it may be difficult to compare data generated at different laboratories. Interlaboratory variation in signature analysis is a common and vexing problem in this field; for this reason, the DEA has centralized its signature programs at a single, specialized laboratory.

To prepare a sample for GC/MS analysis, the dried plant material was extracted with solvent, and then a portion of the extract was diluted with additional solvent to produce a test sample ready to be injected into the instrument. Of the compounds extractable using that method, only a portion of those were detectable under the particular GC/MS conditions used in the study. Although all of the 175 compounds making up the standardized fingerprints could not be specifically identified (even though the spectral evidence suggested some possibilities), each was numbered for reference.

For the study to be complete, however, it was necessary to identify as many of the compounds as possible to better grasp the relationships of the chemical fingerprints to their environs. Several techniques were employed in order to understand the makeup of the chemical fingerprints.

Table 1

Chemical Compounds Identified in a Phase II Study

Table 1

Chemical Compounds Identified in a Phase II Study

Compound

Peak

Compound

Peak

Terpenes

Cannabinoids

Allo-aromadenrene

61

Cannabichromene

17

a-ds-Bergamotene

3

Cannabicitran

48

a-trans-Bergamotene

5

Cannabicumaronone

41

a-Bisabalol

77

Cannabicyclol

15

P-Caryophyllene

4

Cannabidiol

16

Caryophyllene oxide

23

Cannabielsoin

97

a-Cedrene

84

Cannabifuran

44

Curcumene

153

Cannabigerol

32

y-Eudesmol

101

Cannabinol

19

Eupatorio chromene

112

Cannabiviran

167

a-Quaine

85

Dehydrocannabifuran

168

Guaiol

100

A8-Tetrahydrocannabinol

31

a-Humulene

6

A9-Tetrahydrocannabinol

18

Isoledene

132

Tetrahydrocannabinol-^

51

Longifolene

2

Tetrahydrocannabiorocal

105

ds-Nerolidol

92

Tetrahydrocannabiviran

14

irans-Nerolidol

69

Sativene

83

Noncannabinoid phenols

a-Selinnene

66

Cannabispiran

30

a-Terpineol

107

Dehydrocannabispiran

58

Valencene

152

a-Zingeberene

Palmitic acid methyl ester

38

Hydrocarbons

Oleicacid methyl ester

56

Heptacosane

57

Linoleic acid methyl ester

140

Nonacosane

Butylated hydroxytoluene

130

A 1988 study provided information to identify most of the cannabinoids based on retention time and mass spectra (34), but other components were more elusive. Because many of the compounds have almost identical mass spectra and can only be positively identified by GC/MS using a pure reference standard of that compound to establish the retention time on a particular instrument, as many reference standards as could be obtained within the scope of the study were analyzed.

The terpenes were of great interest because their production by plants was likely to consistently reflect the immediate environment, whereas the cannabinoids would tend to reveal genetic relationships. A commercial GC/MS data library (35) was available in both digital and print formats to help identify many of the terpene compounds.

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