CBG: The Key to Cannabis Trichome Chemistry

CBG: Cannabigerol

Often ignored, cannabigerol (CBG) is the precursor for the cannabinolic compounds. In the trichome it is rapidly chemically transformed into tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabichromene (CBC). However, once this precursor compound is created and moved into the secretory reservoir of the trichome, it is never found in high concentrations in the finished weed, yet this critical precursor has medical applications for treating glaucoma, multiple sclerosis and skin disease.

It is rarely found in the finished sativa or indica cannabis plants, but it is found in high amounts in certain strains of industrial hemp that carry a genetic mutation, which down regulates the production of CBD, thereby encouraging the accumulation of CBG. Down regulation is a genetic issue and specifically the lack of the production of proteins.

The primary compound formed in the trichomes is cannabingerolic acid (CBGA)—in molecular variations determined by the various concentrations of terpenes; it creates the fragrance of weed. As can be seen in a chemical analysis of strains ACDC and Harlequin, the amounts of final cannabinolic compounds are determined by the amounts of the specific terpenes created by the genetics of the plant in the plastidic pathways of the disc cells in the trichomes.

For instance, alpha-pinene in Harlequin is higher than in ACDC and the THCV level is higher as well. D-limonene is higher in Harlequin and so are the CBC levels. Linalool is higher in ACDC and so is the CBN content compared to Harlequin. Low alpha-pinene relates to high CBD, low D-limonene relates to high CBD, and beta-myrcene is mapped to the residual amount of CBG, albeit in very low amounts but still in the final product.

This is pretty good evidence that the fragrance of weed—the terpene esters—are scent guides we can all use to identify strains for medical application of cannabis. Smell the weed in the jars at your dispensary before buying, folks—it does a body good!

The Complex Chemistry of Trichomes

So how does this all work? How is this complex chemistry achieved in the trichomes? In an earlier article I presented a study conducted from Spain that proved the production of THC is manganese-dependent while the production of CBD is iron-dependent. That study didn’t delve deep enough into the molecular requirements of mineral substrates to fully describe how these compounds are mineral-dependent. The process begins with light, heat or both.

Under the influence of prolonged UVB during the maturity of the trichomes from clear to milky, CBGA will lose a carbon dioxide molecule. Once this occurs, the plant’s natural enzymes (synthases) break CBG down.

One well-known direction employs CBD synthase to transform CBGA into CBDA, which loses a carbon dioxide molecule to become CBD in the trichomes. When any of the cannabinoid acids—CBCA, THCA and CBDA—are heated (smoked or exposed to UVB), they break down into the neutral forms: CBC, THC and CBD, and at any given time a trichome is filled with a mixture of all these acids and neutral forms.

An article in the Journal of Biological Chemistry from 1996 described an experiment that performed a biochemical analysis of an oxidoreductase, an enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid—CBGA to CBDA. In biochemistry an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor.

These electron transfers are necessary to transform the shape and attraction forces of atoms of the molecules involved to change shape, remove parts and transform into new molecules.

Cannabinoids are plant-secondary metabolites possessing alkylresorcinol (typically olivetol or olivetolic acid) and monoterpene groups in their molecules. This means that the phenols (olivetolic acid) that combine with terpenes (such as in the case of CBG—geranyl pyrophosphate [GPP]).

Read also:

• Essential Oils, Glandular Trichomes & the Secondary Metabolism
• Exploring the Cannabis Entourage Effect
• The Other Cannabinoids: THC-V-, CBD-V-, and CBG-rich Cannabis

Secondary Metabolites

These secondary metabolites then change under the influence of heat or UVB in the trichome secretory reservoir when a carbon dioxide molecule is released. That’s why cannabis grown in the sun is typically higher potency than weed grown indoors unless the growroom has UVB light frequencies provided during the bloom phase.

The heat and light causes this breakdown process to proceed. What the authors verified was that CBDA synthase is an oxidoreductase that catalyzes the cyclization of the monoterpene moiety (the lesser part) in CBGA.

Moiety means that the action is on the terpene part of the molecule. Most terpene cyclases require a divalent ion such as Fe²⁺ or Mn²⁺ for the cyclization of substrates as discovered in an earlier study entitled Biosynthesis and Catabolism of Monoterpenoids by Rodney Croteau from Chem. Rev. in 1987.

This means that the terpene part of the CBG molecule or the subsequent CBD molecule is the means for the synthase enzymes to transform the molecular structures. More specifically, the mineral ions act as a charged region (substrate) for the enzymes to orient around to transform the terpene part of the molecule under the action of the enzyme. Similarly, ionic minerals in the soil do the same thing, acting as pseudo-enzymatic substrates for soil metabolic activity.

This is the same force used for Mn²⁺ to transform CBD into THCA, which then will lose a carbon dioxide molecule in the influence of heat and UVB in the trichome to become THC. However, this can’t happen if the iron or manganese isn’t in the trichome, as shown in the Spanish study identifying these ions as essential for the production of CBD and THC.

What does this all indicate? It shows that there are several terpene-moderated variations of CBG acid molecules that determine the amounts of the various cannabinolic compounds found in the trichomes, and you can smell the differences. It is important to note that it is boron’s unbalanced electron in the 2p shell that can hold calcium and together drag the substrate ions into the trichome to be released to perform the ionic substrate function.

It is essential for the 7:1 calcium-magnesium ratio to be correct in the grow medium. This ratio is an essential part of the nutrient supplementation along with the other critical minerals in the ionic charged state to direct calcium and act as the mineral substrates for the synthase enzymes to convert the precursors into the active compounds in cannabis.