Classification
Bufotenin, a poison from some toads, contains an indole core and is produced in living organisms from the amino acid tryptophan.
The nicotine molecule contains both pyridine (left) and pyrrolidine rings (right). Compared with most other classes of natural compounds, alkaloids are characterized by a great structural diversity and there is no uniform classification of alkaloids.[24] Historically, first classification methods combined alkaloids by the common natural source, e.g., a certain type of plants. This classification was justified by the lack of knowledge about the chemical structure of alkaloids and is now considered obsolete.[5][25] More recent classifications are based on similarity of the carbon skeleton (e.g., indole, isoquinoline and pyridine-like) or biogenetic precursor (ornithine, lysine, tyrosine, tryptophan, etc.).[5] However, they require compromises in borderline cases;[24] for example, nicotine contains a pyridine fragment from nicotinamide and pyrrolidine part from ornithine[26] and therefore can be assigned to both classes.[27] Alkaloids are often divided into the following major groups:[28] 1. "True alkaloids", which contain nitrogen in the heterocycle and originate from amino acids.[29] Their characteristic examples are atropine, nicotine and morphine. This group also includes some alkaloids which beside nitrogen heterocycle contain terpene (e.g. evonine[30]) or peptide fragments (e.g. ergotamine[31]). This group also includes piperidine alkaloids coniine and coniceine[32] although they do not originate from amino acids.[33] 2. "Protoalkaloids", which contain nitrogen and also originate from amino acids.[29] Examples include mescaline, adrenaline and ephedrine. 3. Polyamine alkaloids – derivatives of putrescine, spermidine and spermine. 4. Peptide and cyclopeptide alkaloids.[34]
5. Pseudalkaloids – alkaloid-like compounds which do not originate from amino acids.[35] This group includes, terpene-like and steroid-like alkaloids,[36] as well as purine-like alkaloids such as caffeine, theobromine and theophylline.[37] Some authors classify as pseudoalkaloids such compounds such as ephedrine and cathinone. Those originate from the amino acid phenylalanine, but acquire their nitrogen atom not from the amino acid but through transamination.[37][38] Some alkaloids do not have the carbon skeleton characteristic of their group. So, galantamine and homoaporphines do not contain isoquinoline fragment, but are generally attributed to isoquinoline alkaloids.[39] Main classes of monomeric alkaloids are listed in the table below: Class
Major groups Main synthesis steps Alkaloids with nitrogen heterocycles (true alkaloids)
Pyrrolidine derivatives[40]
Tropane derivatives[43]
Ornithine or arginine → putrescine → NHygrine, hygroline, methylputrescine → stachydrine[40][42] N-methyl-Δ1pyrroline [41] Atropine, Ornithine or arginine scopolamine, Substitution in positions 3, 6 or → putrescine → N- hyoscyamine[40][43][44] 7 methylputrescine → N-methyl-Δ1Cocaine, ecgonine [43] Cocaine group [41] [45] Substitution in positions 2 and 3 pyrroline Atropine group
Non-esters Pyrrolizidine derivatives[46]
Complex esters of monocarboxylic acids Macrocyclic diesters 1-aminopyrrolizidines (lolines)
Piperidine derivatives[51]
Examples
Retronecine, In plants: ornithine or heliotridine, laburnine [46][47] arginine → putrescine → Indicine, lindelophin, homospermidine → sarracine [46] retronecine [41] Platyphylline, trichodesmine[46] In fungi: L-proline + L-homoserine → N- Loline, N(3-amino-3formylloline, Ncarboxypropyl)prolin acetylloline[50] e → norloline[48][49] Sedamine, lobeline, Lysine → cadaverine anaferine, piperine → Δ1-piperideine [52] [32][53] Octanoic acid → Coniine, coniceine coniceine → coniine [33] [33]
Lupinine group Quinolizidine derivatives[54][55]
Cytisine group Sparteine group Matrine group Ormosanine group
Indolizidine derivatives[60]
Simple derivatives of pyridine
Lupinine, nupharidin [54]
Cytisine [54] Sparteine, lupanine, Lysine → cadaverine anahygrine[54] → Δ1-piperideine [56] Matrine, oxymatrine, allomatridine[54][57][58] Ormosanine, piptantine[54][59] Lysine → δsemialdehyde of αSwainsonine, aminoadipic acid → castanospermine [62] pipecolic acid → 1 indolizidinone [61] Trigonelline, ricinine, arecoline [63] [66]
Nicotinic acid → Nicotine, Polycyclic noncondensing digidronikotinovaya nornicotine, pyridine derivatives acid → 1,2anabasine, anatabine dihydropyridine [65] [63][66] Actinidine, Polycyclic condensed gentianine, pyridine derivatives pediculinine [67] Evonine, Sesquiterpene pyridine Nicotinic acid, hippocrateine, derivatives isoleucine [11] triptonine [64][65] Isoquinoline Simple derivatives of Tyrosine or Salsoline, [69] derivatives and isoquinoline phenylalanine → lophocerine [68][69] related alkaloids dopamine or N-methylcoridaldine, Derivatives of 1- and 3[68] tyramine (for noroxyhydrastinine isoquinolines [72] alkaloids Amarillis) [72] [70][71] Derivatives of 1- and 4phenyltetrahydroisoquinoli Cryptostilin [69][73] [69] nes Derivatives of 5-naftilAncistrocladine [74] isoquinoline [74] Papaverine, Derivatives of 1- and 2laudanosine, benzyl-izoquinolines [75] sendaverine Cularine, yagonine Cularine group[76] [76] Pyridine derivatives[63][64]
Pavines and isopavines [77] Benzopyrrocolines [78]
Argemonine, amurensin [77] Cryptaustoline [69]
Protoberberines [69] Phtalidisoquinolines [69] Spirobenzylisoquinolines [69]
Ipecacuanha alkaloids
[81]
Benzophenanthridines [69] Aporphines [69] Proaporphines [69] Homoaporphines [84] Homoproaporphines [84] Morphines[85]
Berberine, canadine, ophiocarpine, mecambridine, corydaline [79] Hydrastine, narcotine (Noscapine) [80] Fumaricine [77] Emetine, protoemetine, ipecoside [81] Sanguinarine, oxynitidine, corynoloxine [82] Glaucine, coridine, liriodenine [83] Pronuciferine, glaziovine [69][78] Kreysiginine, multifloramine [84] Bulbocodine [76] Morphine, codeine, thebaine, sinomenine [86]
Phenanthrene derivatives
Kreysiginine, androcymbine [85] Imerubrine [69] Rufescine, imeluteine [88] Lycorine, ambelline, tazettine, galantamine, montanine [90] Erysodine, erythroidine [73] Atherosperminine [69]
[69]
[79]
Homomorphines [87] Tropoloisoquinolines [69] Azofluoranthenes [69] Amaryllis alkaloids[89] Erythrite alkaloids[73]
Protopins
[69]
Aristolactam [69] Oxazole derivatives[91]
Protopine, oxomuramine, corycavidine [82] Doriflavin [69] Tyrosine → tyramine Annuloline, [92] halfordinol, texaline, texamine[93]
Thiazole derivatives[94]
Quinazoline derivatives[97]
1-Deoxy-D-xylulose 5-phosphate Nostocyclamide, (DOXP), tyrosine, thiostreptone [94][96] cysteine [95] 3,4-Dihydro-4-quinazolone derivatives Anthranilic acid or 1,4-Dihydro-4-quinazolone phenylalanine or derivatives ornithine [98] Pyrrolidine and piperidine quinazoline derivatives
Acridine derivatives[91]
Anthranilic acid [100] Simple derivatives of quinoline derivatives of 2 quinolones and 4quinolone Anthranilic acid → Tricyclic terpenoids 3-carboxyquinoline
Quinoline derivatives[103][104] Furanoquinoline derivatives
[105]
Febrifugine[99] Glycorine, arborine, glycosminine[99] Vazicine (peganine) [91]
Rutacridone, acronicine[101][102] Cusparine, echinopsine, evocarpine[104][106][107] Flindersine[104][108] Dictamnine, fagarine, skimmianine[104][109] [110]
Indole derivatives[86]
Tryptophan → tryptamine → Quinine quinidine strictosidine (with Quinines cinchonine, secologanin) → cinhonidine [108] korinanteal → cinhoninon [71][105] Non-isoprene indole alkaloids Tryptophan → Serotonin, tryptamine or 5psilocybin, Simple indole derivatives [112] hydroxitriptofan dimethyltryptamine [111] (DMT), bufotenin [113][114]
See also: indole
Simple derivatives of βcarboline [115]
Harman, harmine, harmaline, eleagnine
[111]
alkaloids
Physostigmine (eserine), Pyrroloindole alkaloids [116] etheramine, physovenine, eptastigmine[116] Semiterpenoid indole alkaloids Tryptophan → chanoclavine → Ergotamine, agroclavine → Ergot alkaloids[86] ergobasine, elimoclavine → ergosine[117] paspalic acid → lysergic acid [116] Monoterpenoid indole alkaloids Ajmalicine, sarpagine, vobasine, ajmaline, yohimbine, reserpine, Corynanthe type mitragynine [118][119], alkaloids[112] group strychnine and Tryptophan → (Strychnine brucine, tryptamine → aquamicine, strictosidine (with vomicine [120]) secologanin) [112] Ibogamine, ibogaine, Iboga-type alkaloids[112] voacangine[112] Vincamine, Aspidosperma-type vincotine, alkaloids[112] aspidospermine[121] [122]
Imidazole derivatives[91]
Directly from histidine[123]
Histamine, pilocarpine, pilosine, stevensine[91][123]
Xantosine (formed in purine biosynthesis) Caffeine → 7 methylxantosine theobromine → 7-methyl xanthine theophylline → theobromine → saxitoxin [125][126] caffeine [71] Alkaloids with nitrogen in the side chain (protoalkaloids) βTyrosine or Tyramine, ephedrine, Phenylethylamine phenylalanine → pseudoephedrine, [78] derivatives dioxyphenilalanine mescaline, cathinone, → dopamine → catecholamines Purine derivatives[124]
adrenaline and mescaline tyrosine → tyramine phenylalanine → 1- (adrenaline, phenylpropane-1,2- noradrenaline, dione → cathinone dopamine)[11][128] → ephedrine and pseudoephedrine [11] [38][127]
Colchicine alkaloids [129]
Muscarine [131]
Benzylamine[133]
Tyrosine or phenylalanine → dopamine → autumnaline → colchicine [130]
Colchicine, colchamine[129]
Glutamic acid → 3ketoglutamic acid → muscarine (with pyruvic acid)[132]
Muscarine, allomuscarine, epimuscarine, epiallomuscarine[131]
Phenylalanine with valine, leucine or isoleucine[134]
Capsaicin, dihydrocapsaicin, nordihydrocapsaicin [133][135]
Polyamines alkaloids Putrescine derivatives[136] Spermidine derivatives[136] Spermine derivatives[136]
Peptide alkaloids with a 13membered cycle [34][138]
Peptide alkaloids with a 14membered cycle [34][138]
Paucine [136] ornithine → putrescine → spermidine → spermine[137]
Lunarine, codonocarpine[136] Verbascenine, aphelandrine [136]
Peptide (cyclopeptide) alkaloids From different amino Numularine C, Numularine C type acids [34] numularine S [34] Ziziphin A, Ziziphin type sativanine H [34] Frangulanine, Frangulanine type scutianine J [138] Scutianine A type Scutianine A [34] Integerrine type Integerrine, discarine
D [138] Amphibine F, spinanine A [34] Amphibine B, lotusine C [34]
Amphibine F type Amfibine B type Peptide alkaloids with a 15Mucronine A type membered cycle
Mucronine A [31][138]
[138]
Diterpenes
[31]
Pseudoalkaloids (terpenes and steroids) Mevalonic acid → izopentenilpyrophosf Aconitine, delphinine Licoctonine type [31][141] ate → geranyl [139][140] pyrophosphate
Steroids[142] Cholesterol, arginine[143]
Solasodine, solanidine, veralkamine[144]