Simply, phytochemicals are naturally occuring molecules found in plants. They are the principle substances that are responsible for their pigmentation, essence, and flavor. Thousands of phytochemicals have been identified so far, and scientists have only begun to investigate their promise. The following chart (Table 1.) lists some of the phytochemicals attracting serious scientific attention, identifies food sources and outlines potential benefits.1

Phytochemicals
Phytochemical(s)
Plant Source
Possible Benefits
Carotenoids
(such as beta-carotene, lycopene, lutein, zeaxanthin)
Red, orange and green fruits and vegetables including broccoli, carrots, cooked tomatoes, leafy greens, sweet potatoes, winter squash, apricots, cantaloupe, oranges and watermelon May inhibit cancer cell growth, work as antioxidants and improve immune response
Flavonoids
(such as anthocyanins and quercetin)
Apples, citrus fruits, onions, soybeans and soy products (tofu, soy milk, edamame, etc.), coffee and tea May inhibit inflammation and tumor growth; may aid immunity and boost production of detoxifying enzymes in the body
Indoles and Glucosinolates
(sulforaphane)
Cruciferous vegetables (broccoli, cabbage, collard greens, kale, cauliflower and Brussels sprouts) May induce detoxification of carcinogens, limit production of cancer-related hormones, block carcinogens and prevent tumor growth
Inositol
(phytic acid)
Bran from corn, oats, rice, rye and wheat, nuts, soybeans and soy products (tofu, soy milk, edamame, etc.) May retard cell growth and work as antioxidant
Isoflavones
(daidzein and genistein)
Soybeans and soy products (tofu, soy milk, edamame, etc.) May inhibit tumor growth, limit production of cancer-related hormones and generally work as antioxidant
Isothiocyanates Cruciferous vegetables (broccoli, cabbage, collard greens, kale, cauliflower and Brussels sprouts) May induce detoxification of carcinogens, block tumor growth and work as antioxidants
Polyphenols
(such as ellagic acid and resveratrol)
Green tea, grapes, wine, berries, citrus fruits, apples, whole grains and peanuts May prevent cancer formation, prevent inflammation and work as antioxidants
Terpenes
(such as perillyl alcohol, limonene, carnosol)
Cherries, citrus fruit peel, rosemary May protect cells from becoming cancerous, slow cancer cell growth, strengthen immune function, limit production of cancer-related hormones, fight viruses, work as antioxidants

(Table 1. - Phytochemicals : Class, Source, and Potential benefits.) 

Source: American Institute for Cancer Research, Phytochemicals: The Cancer Fighters In Your Food, American Institute for Cancer Research, Aug. 2017, table 1.

With so much attention being focused on cannabis lately let's look at one of the more promising cannabinoids with pharmaceutical utility, cannabidiol (CBD). One may pose the question where does CBD come from? As earlier stated it is a naturally occurring compound present in varieties of Cannabaceae C.. Here's how CBD is created. Its not all done with in the plant. In fact only the carboxylic acid form of cannabidiol (CBDa) is produced inside the glandular trichome while the plant is growing. The final decarboxylation step is chemically a degradation of the carboxyl functional group, because when CBDa is exposed to heat and/or varying amounts of light, carbon dioxide is liberated along with water and hydrogen replaces the carboxyl functional groups position. The resulting substitution creates CBD.

The biosynthesis of CBDa is a complex series of reactions that begins with the medium chain fatty acid hexanoyl-CoA. For simplicity sake, illustrated below is the sequence of reactions where Geranyl pyrophosphate (GPP) and Olivetolic acid bind in the presence of an enzyme referred to as a Geranylpyrophosphate--olivetolic acid geranyltransferase (GOT) to form CBGa. CBGa is bound by the enzyme CBD synthase and converted to CBDa. Then finally CBDa is decarboxylated via heat and/or light to form CBD.

  Geranyl pyrophosphate (GPP)
                                                     
GOT Enzyme       +    
(Olivetolic Acid)
                                                         
 Cannabigerolic Acid (CBGa)
CBD Synthase
 Cannabidiol Acid (CBDa)
Decarboxylation 


                                                          

 Cannabidiol (CBD)

1 "Phytochemicals: The Cancer Fighters In Your Food." aicr.org . American Institute of Cancer Research, Aug. 2017. Web. 30 Aug. 2017.