What is CBD?
It was at the Noyes Chemical Laboratory at the University of Illinois in 1940 where chemists Roger Adams, Madison Hunt and J.H. Clark first isolated cannabidiol (CBD). Prior to their experiments, cannabinol (CBN) was the only cannabinoid which had been characterized from the cannabis plant. The scientists characterized CBN from samples of hashish sourced from India, and this was the compound they were looking for in wild hemp grown in Minnesota.
The flower tops of hemp were extracted with ethanol and distilled in the lab to give an oil which was red in appearance. The scientists were shocked when they didn’t find any CBN, however qualitative tests indicated that there were other similar compounds (phenols) in the red oil. Furthermore, a long list of qualitative tests were further performed to define the structure of CBD - as analytical chemistry was not as advanced in 1940 as it is today. Adams et al. theorized that there would be many structurally related compounds to CBN and CBD present in cannabis. This turned out to be true as many other compounds, including THC, were later extracted and characterized from the cannabis plant. According to the International Union of Pure and Applied Chemistry (IUPAC) nomenclature of organic chemistry, the chemical name for cannabidiol is 2-[(1R,6R)-3-methyl-6-prop-1-en-2-ylcyclohex-2-en-1-yl]-5-pentylbenzene-1,3-diol. This name (even if it is a bit of a mouthful) describes the precise chemical structure of cannabidiol, naming all the functional groups that are present in the cannabidiol structure.
Antibacterial activity in cannabis alerts scientists to a mystery molecule
Krejčí and Šantavý, at the Palacky´ University at Olomouc in Czechoslovakia, found that an alcohol extract of a cannabis plant showed antibacterial activity. They further demonstrated that that molecule responsible for this antibacterial activity was cannabidiolic acid (CBDA), the precursor to CBD. This was the first acidic cannabinoid discovered in the cannabis plant, and further paved the way to the understanding of the biosynthetic pathway of cannabinoids we know today.
Biosynthesis of CBD
Cannabinoids are produced from the convergence of two pathways; the polyketide pathway (the origin of olivetolic acid) and the plastidic MEP pathway (the origin of geranyl pyrophosphate). An enzyme called geranylpyrophosphate:olivetolate geranyltransferase catalyses the reaction between geranyl pyrophosphate and olivetolic acid to give rise to cannabigerolic acid (CBGA). An oxidocyclase called CBDA synthase performs a stereospecific oxidative cyclization on CBGA to form CBDA. CBDA is then decarboxylated to form CBD. This occurs partially in the plant, as well as part of the manufacturing step in the production of CBD.
Key chemical properties
The two hydroxyl groups on CBD grant it the ability to act as a hydrogen bond donor and acceptor, however there is not enough polarity in the molecule to dissolve in polar solvents such as water. CBD is soluble in organic solvents ethanol, methanol, dimethyl sulfoxide and dimethyl formamide. Conveniently, CBD is also soluble in liquid carbon dioxide - which is an environmentally friendly solvent commonly used in the manufacturing of CBD. The melting point of CBD is 66 celsius, henceforth CBD is a crystalline solid at room temperature. The boiling point is 180 celsius (while the boiling point of THC is 157). Consequently, the vaporization temperature has to be kept at a high temperature (greater than 180 degrees celsius) for those using vaporisation as a medication option, in order for CBD to be transformed into the gaseous state and enter the lungs. Cannabidiol absorbs light in the ultraviolet region and has absorption peaks at 209 and 275 nm respectively. The two peaks are a characteristic of phenolic compounds, and as CBD is a terpenophenolic compound it consequently has maximal absorption of light at those two peaks. When CBD is exposed to light, an electron is promoted highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). As CBD shows two peaks in its UV spectrum, two electron transitions are taking place. The energy of the two electron transitions is proportional to the wavelength of light, according to the equation derived by the founder of theoretical physics - Max Planck.
The colour of any object is determinant on the wavelength of light the object absorbs, transmits and more importantly reflects. As pure CBD crystals are white in colour, it can be deduced that it reflects all the colours of the visible light spectrum (400nm to 700nm) - as white light is the combination of all the different wavelengths of light.
Degradation of CBD and CBDA
In 1974, the prominent cannabinoid scientists Arnon Shani and Raphael Mechoulam isolated two molecules called cannabielsoic acid A (CBEA-A) and cannabielsoic acid B (CBEA-B) from hashish. From further experimentation they deduced that these compounds were formed through the oxidative cyclisation of CBDA, a reaction which is activated by light. Moreover, as time progresses and the cannabis plant is exposed to light of high intensity, CBDA is degraded into CBEA-A or CBEA-B. These degradants form the cannabinoid cannabielsoin (CBE) upon decarboxylation. CBE was identified as a metabolite of CBD in a study conducted on guinea pigs, however no significant pharmacological activity has been noted for this compound till date.