Glossary – phytochemistry (under construction)

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Palmitic acid – a C₁₆-saturated fatty acid found in most fats and oils, particularly associated with stearic acid

Papain – papaya proteinase I; a cysteine protease

Papaverine – an isoquinoline alkaloid

Parasorbic acid – a lactone

Patrinoside – a route II iridoid

Pectin – a highly hydrophilic polysaccharide built up of monomers of α-galacturonic acid, an important component of cell walls

Pedunculagin – a cytotoxic hydrolyzable ellagitannin

Pelargonidin – an anthocyanidin

Pentadin – a sweet-tasting protein present in Pentadiplandra brazzeana

Perinaphthenone – 1-H-phenalene-1-one; a phenylphenalenone

Petroselinic acid – cis-6-octadecenoic acid; a mono-unsaturated fatty acid with the double bond in the δ-6 position

Phaseollin – a phytoalexin that is a kind of isoflavonoid (a pterocarpan)

Phenanthrene – a polycyclic aromatic hydrocarbon consisting of three benzene rings

Phenylethylamine – phenethylamine; a monoamine alkaloid; biosynthesized from phenylalanine

Phenols – acidic aromatic compounds; common constituents of organic compounds

L-Phenylalanine – a non-protein amino acid from which e.g. isoquinoline alkaloids are derived via decarboxylation

Phenylphenalenones – a group of fungitoxic phytoalexins; unique red pigments consisting of the glycoside haemocorin

Phenylpropanoids – any compound bearing a 3-carbon chain attached to a 6-carbon aromatic ring (C6-C3 compounds), most being formed from cinnamic or p-coumaric acids, volatile compounds in essential oils; phenylpropanoid glucosides (e.g. orobanchoside and verbascosides) have a central glucose unit, a C6-C2 unit, often dihydroxyphenyl-β-ethanol and a C6-C3 unit (hydroxycinnamic acid)

Phlobaphene – amorphous yellowish, reddish or brownish material probably anhydrous derivatives of proanthocyanidins or non-hydrolyzable tannins and found e.g. in the testa of some seeds, its colour change is secondary and either enzymic or chemical

Phloroglucinol – simple phenolic compound composed of an aromatic ring and three hydroxyl groups, an aglycone of many glycosides

Phorbol – a polycyclic alcohol present in croton oil, the parent compound of the phorbol esters, potent cocarcinogens; phorbol esters are diterpenes

Physostigmine – eserine; a parasympathomimetic alkaloid, present in some Fabaceae

Phytoalexins – a general term referring to substances that inhibit further development of a fungus in hypersensitive host tissue (also antimicrobial), the first one isolated was an isoflavan, others are sesquiterpenes, etc.

Phytomelan – black, inert C-rich carbonaceous material lacking nitrogen, probably derived from catechol, that forms a crust-like covering of some seeds, frequent in Asparagales

Pinitol – a cyclitol (cyclic polyol)

Pinoresinol – a lignan

Piptoside – P-D-glucopyranoside

Plumbagin – 5-hydroxy-2-methyl-1,4-naphthoquinone, a toxin derived from naphthoquinone

Polyacetylenes – unsaturated compounds derived from oleic acid by dehydrogenation, highly reactive but with additional functional groups such as alcohols, ketones, acids, esters, furans, or pyrans which tend to stabilize the reactive acetylenic bonds

Polyfructosans – fructose polysaccharides, e.g. inulin

Polygalitol – 1,5-anhydro-D-glucitol, 1,5-sorbitan; an anhydride of sorbitol, present in, e.g., Polygala

Polyhydroxy alkaloids, indolizidine alkaloids – bicyclic alkaloids with fused 5- and 6-membered ring systems

Polyisoprenes – high molecular-weight terpenoids made up of many isoprene units, e.g. rubber

Polyketides – compounds related to fatty acids composed of condensed acetate and malonate units with unreduced carbonyl units and aromatic ring systems, typically with phenolic substitutions

Polyol – a carbohydrate produced directly or indirectly by the reduction of aldose or ketose sugars, there are at least three carbon atoms each with an -OH group

Prenylation – the attachment of a prenyl or isoprene unit, as in prenylated naphthoquinones

Primitive tannins – see Proanthocyanidins

Proanthocyanidins – polymeric tannins, non-hydrolyzable tannins, “condensed” tannins; colourless glycosidic anthocyanidins, derived from isomerized flavonoids, usually polymers and based on monomeric flavan-3-ol (catechins) and flavan-3,4-diol units, colourless compounds that yield red anthocyanidins upon heating with acid (not precursors to anthocyanidins in plants); proanthocyanidins are produced from cinnamic acid and tend to show an inverse distribution relative to caffeic acid; an example is leucocyanidin hydrate

Prodelphinidin – polymeric tannins composed of gallocatechin

Proteacin – a cyanogenic glycoside

Protoalkaloid – an alkaloid derived from amino acids, but lacking a heterocyclic ring, the nitrogen being present elsewhere in the molecule

Prunasin – a cyanogenic glucoside

Pseudoalkaloids – alkaloids in which the basic carbon skeleton is derived from terpenes, sterols, aliphatic acids, nicotinic acid, or purines rather than amino acids

Psoralen – a fur(an)ocoumarin; a derivative of umbelliferone

Pterocarpans – isoflavonoids that are derived from isoflavones via oxygenation of the 2’-position

Punicic acid – trichosanic acid; a polyunsaturated fatty acid, a conjugated linolenic acid, present in some Cucurbitaceae, Punica etc.

Pyranochromones – class of chromones which are isomers of pyranocoumarins

Pyridine – a toxic, colourless, liquid, aromatic hydrocarbon comprising a substituted benzene ring; pyridine alkaloids are true alkaloids with the parent base being pyridine or lysine; examples of pyridines include nicotine, anabasine, anatabine, and ricinine

Pyrrolidine – tetramethylene imine; pyrrolidine alkaloids have a five-membered nitrogen-containing ring

Pyrrolizidine alkaloids – a group of alkaloids, based loosely on tropane, via ornithine, containing two fused 5-membered rings with a nitrogen at one of the common positions; pyrrolizidine alkaloids include, e.g., heliotridine, retronecine, heliosupine, senecionine, monocrotaline, trichodesmine, and otonecine