Prunin is a flavanone glycoside found in immature citrus fruits and in tomatoes. Its aglycone form is called naringenin.
Flavonoid biosynthesis in plants uses a phenylpropanoid metabolic pathway in which the amino acid phenylalanine is converted to 4-coumaroyl-CoA. This is combined with three units of malonyl-CoA to yield a group of compounds called chalcones, which contain two phenyl rings. In the main pathway, the enzymes chalcone synthase and chalcone isomerase produce (S)-naringenin which is the immediate precursor for prunin.
Flavanone 7-O-beta-glucosyltransferase uses UDP-glucose to transfer a sugar group to one of the phenolic hydroxyl groups of (S)-naringenin.
In some citrus fruits, the product prunin is converted to naringin, a compound which is responsible for the bitter taste of grapefruit.
Flavanone 7-O-glucoside 2"-O-beta-L-rhamnosyltransferase uses UDP-rhamnose to add the second sugar component.
Glucosidase breaks dietary prunin back into glucose and naringenin.