Terrestrial Natural Product Chemistry

Phenolic compounds are characterized by phenol and hydroxyl substituents.
Over 8,000 phenolic compounds have been isolated and characterized.
Important groups include flavonoids, quinones, xanthones, depside/depsidone, coumarin, and phenylpropanoid derivatives.

Phenolic compounds contribute to the taste, flavour, and colour of food and drinks.
Tea contains ~30% polyphenolic compounds, and ribena drinks get their color from anthocyanins like malvin.
Phenolics play a role in protecting plants from herbivores through phytoalexins and phytoanticipins.
They serve as chemical signals for flowering and pollination.

Various chemical structures were shown as examples (phenols, p-coumaric acid, ubiquinol, ferulic acid, catechol, etc).
Additional structures of important compounds like vitamin E, capsacin, gallic acid (G), and others were presented.
Chemical structures of various phenolic compounds were displayed.

A table displaying phenolic compounds categorized based on the number of C atoms and their basic skeleton was shown.
The classes included simple phenols, benzoquinones, phenolic acids, acetophenone, phenylacetic acid, hydroxycinnamic acid, polypropene coumarin, isocoumarin, naphthoquinone, xanthone, stilbene, anthraquinone, flavonoids, isoflavonoids, lignans, neolignans, and biflavonoids.

A table depicted the distribution of phenolics across various phyla, including bacteria, fungi, algae, lichens, bryophyta, ferns, conifers, and flowering plants.
Bacteria produce polyketide-derived phenols and quinones.
Fungi and algae exhibit simple phenols, phenylpropanoids, and quinones.

Flavonoids are the largest class of phenolic compounds with wide distribution in plants.
They exhibit diverse molecular structures and hydroxylation patterns.
A table highlighting important classes of flavonoids and their biological significance, including anthocyanins, chalcons, aurones, and flavones, and their associated numbers of known members, and descriptions of their effects.

Flavonoids are important dietary antioxidants and significant components of medicinal herbs.
Flavonoids, including anthocyanins, proanthocyanidins, and flavanols, are the most abundant antioxidants in the diet.
Fruits such as blueberries, blackberries, strawberries, raspberries, and eggplant are rich in flavonoids. Other sources include onions, garlic, and cocoa powder.
Flavonoids are involved in protecting tissue against oxidative stress, acting as preventative medicines for cardiovascular diseases, cancers, arthritis, and autoimmune disorders.

Two types of glycoside bonds are found in flavonoids: O-glycosides (weaker bonds that can be hydrolyzed by dilute acid) and C-glycosides (stronger bonds that don't hydrolyze with dilute acid).
Common sugars attached include glucose, rhamnose, arabinose, and xylose.

Flavonoids can be detected by different color reactions after reacting with various solutions or substances, depending on the kind of flavonoid.

Anthocyanidins (aglycones) and anthocyanins (glycosides) have structures similar to the flavan nucleus.
They differentiate by having a positive charge on the oxygen and double bonds in the C ring.

Proanthocyanidins, sometimes called condensed tannins, are responsible for astringency in many foods and medicinal herbs.
They are complex proanthocyanidins and can be found in grape skins, seeds, blueberries, blackberries, strawberries, and other red/purple plant parts.
Proanthocyanidins are antioxidants that contain oligomers from multiple flavonoid molecules.
Subunits of proanthocyanidins are often linked in different ways forming large structures.

Isoflavones are similar to flavones with the B ring attached to position 3 of the C ring instead of position 2.
Genistein is an important isoflavone found in red clover, alfalfa, peas, soy, and other legumes, protective against breast, prostate, and colon cancers, and can help with osteoporosis prevention.
Daidzein is very similar to genistein but lacks the -OH group at position 5.
Isoflavone compounds like formononetin and biochanin A are found in red clover, and are similar to daidzein and genistein.

Flavonols have an -OH group attached to position 3 of the basic flavan skeleton and a double bond between carbons 2 and 3 on the C ring.
Quercetin is the most abundant flavonol in many foods and herbs. It exhibits antioxidant effects.

Flavones are similar to flavonols except there is no longer an -OH group at position 3 on the central ring.
Apigenin and luteolin are important flavones found in celery and sweet red peppers, respectively.

Flavanones lack the double bonds between carbons 2 and 3.
Naringenin, a flavanone found in citrus fruits, has antioxidant, anti-inflammatory, anti-cancer, and liver-protective effects.
Hesperetin and Hesperidin are also flavanones commonly found in some citrus.

The A-ring forms from three acetate units through the malonic acid pathway.
The B-ring, including the 3-carbon bridge, is derived from a phenylpropane unit via the shikimic acid pathway.
Chalcone synthase plays a critical role in the synthesis of other flavonoid types.

Flavonoids can be detected through colorimetric reactions involving reagents like hydrochloric acid or magnesium ribbon.
TLC/PC methods can also be used for analysis using known standards.

Flavonoid's antioxidant capacity is linked to the degree of hydroxylation on the B-ring.
Increased hydroxylation results in higher antioxidant capacity, as seen with epigallocatechin, epicatechin gallate, and epigallocatechin gallate.
The trend of increased antioxidant value is also observed with anthocyanidins like pelargonidin, cyanidin, and delphinidin.

Flavonoids are widely distributed in plants, performing various functions including producing pigments in flowers and protection from insects and microbes.
Flavonoids' relative low toxicity levels and widespread distribution mean many animals and humans ingest significant amounts in their diet.
They have been linked to protection for allergies, viruses, carcinogens, and related effects with antioxidant roles.
Consumers and food manufacturers are increasingly attentive to the medical properties of flavonoids, focusing on their roles in cancer and cardiovascular disease prevention.