## 3 Biosynthesis and Health Implications of Tropane Alkaloids
### Biosynthesis of Tropane Alkaloids  
Over the past 200 years, researchers worldwide have shown much interest in the tropane alkaloids (TAs) class. Since 1830 onward, when the first chemical isolations of TAs started with atropine from _Atropa belladonna_, hyoscyamine from _Hyoscyamus niger_, and scopolamine from _Scopolia japonica_, then followed in 1860 by cocaine's isolation from _Erythroxylum coca_, these molecules have had an extensive usage in clinical medicine for their peculiar biological proprieties and distinct physiological effects in humans. The biosynthetic pathway of tropane alkaloids involves a complex coordination of independence enzymes which catalyze sequential reactions which also undergo a wide evolutionary diversification among species [26]. For example, [PERSON] and colleagues (2023) compared the genomes of _Erythroxylum novogranatense_ (Erythroxylaceae) and _Anisodus actantgulus_ (Solanaceae) to understand at a genetic and structural level the evolutive changes in key enzymesresponsible for the structural differences in tropane alkaloid (TA) formation as for cocaine and hyoscyamine [21; 27]. The distinctive evolutionary pathway between Solanaceae and Erythroxylaceae, besides divergence in TAs molecules formation and distinct enzymatic reaction, relies also on a different biosynthetic location. So far, the biosynthesis of tropane alkaloids in Solanaceae takes place in roots and then TAs are translocated to the aerial parts, whereas in Erythroxylaceae, TA formation and storage occurs in the leaves [18; 21]. Tropane alkaloids consist of more than 200 known compounds in various plants, and the biosynthesis of the tropane ring formation is a shared route. The biosynthesis of the TAs starts with the decarboxylation of the amino acids ornithine or arginine by ornithine decarboxylase (ODC, EC 4.1.1.17) or arginine decarboxylase (ADC, EC 4.1.1.19) to form the polyamine putrescine. Mono-methylation of putrescine via methyltransferase (PMT, EC 2.1.1.53) leads to N-methylputrescine. Then, oxidation of the primary amino group by diamine oxidase (DAO, EC 1.4.3.22) yields 4- (methyl-1-amino) butanal. Next, spontaneous cyclization dehydration takes place, with the formation of the reactive N-methyl-\(\Delta\)-1-pyrrolidin cation which is the precursor of all TAs. This monocyclic precursor is further converted into a corresponding 4-carbon side chain \(\beta\)-ketoacid intermediate by the action of two acetyl coenzyme A (AcCoA) ester molecules. The oxobutanoic acid can cyclize to exo-carboxy tropinone. Then the tropinone can be the substrate to produce both/either tropine (3\(\alpha\)-tropinol) by tropinone reductase (TR I, EC 1.1.1.206) and/or pseudotropine (3\(\beta\)-tropinol) by tropinone reductase (TR II, EC 1.1.1.236) [28]. Structural differences among TAs derive from the tropine esterification with a variety of acids which are opportunely classified based on the number of carbons in the tropane skeleton and stereochemical conformation. Hydroxylation at the C3 position of tropane determines two stereoisomers, tropine (3\(\alpha\)-tropanol) and pseudotropine (3\(\beta\)-tropanol), depending on the orientation (\(\alpha\) or \(\beta\)) of the hydroxyl group [29]. The activity of TR I leads to the most well-known TAs, hyoscyamine, atropine, and scopolamine. In detail, TR I esterified tropine with phenyllactic acid producing littorine, which in turn isomerizes to form hyoscianine. Subsequently, hyoscyamine can be transformed into scopolamine via the enzymatic activity of hyoscyamine 6\(\beta\)-hydroxylase (H6H) [30]. TRII leads to the formation of calystegines through pseudotropine. Calystegines are polyhydroxylated nortropane alkaloids (NTAs) whose structure consists of the single tropane ring with three to five hydroxyl groups in various positions that are divided into three principal groups (groups A, B, and C) [31]. High levels of group A and B calystegines were found in food from the Solanaceae family, such as potatoes, peppers, paprika, and eggplants.