Alkaloids are nitrogen-containing small molecules which are mainly found in plants.¹⁾ To date, approximately 27 thousand alkaloids have been reported in which 21 thousand were of plant origin.
Since most of the alkaloids exhibit potent bioactivity, they are the main component of many herbal medicines. Some alkaloids are also used as pharmaceuticals. Alkaloids interact with proteins electrostatically due to the positive charge of the nitrogen atoms which facilitates binding to the negative charge of the proteins. Especially, pharmaceutical alkaloids tend to bind to the receptors in neural systems.

■Biosynthesis
Biosynthetic pathways to alkaloids vary greatly depending on the nitrogen source. Alkaloids are biosynthesized from various kinds of amino acids as depicted in Fig. 1. Further complex alkaloids are also biosynthesized by attaching another alkaloid to the original skeletons.

■Structure Classification
In the IUPAC Nomenclature Appendix, 67 alkaloid parent structures are shown.²⁾ They can be classified into their basic skeletons based on their biosynthetic origins as shown in Fig. 1. In this section, alkaloids are categorized into nine: eight as shown above and purine alkaloids as the ninth. Polyamines which are occasionally considered as alkaloid-related substances, will be explained in the section “Polyamines”.

■Solubility
In general, alkaloids dissolve in acidic water. Their salts dissolve in neutral water. They are usually insoluble in neutral water as free forms, but soluble in polar organic solvents such as chloroform, methanol or DMSO.

■Analysis
HPLC：In the reversed phase mode using an ODS column, peak tailing is suppressed by addition of acetic acid or trifluoroacetic acid to the mobile phase. Effective analysis would be achieved by a mixed mode column, TCI-Dual, with ion-exchange and reversed phase modes simultaneously. Detection is generally conducted by a UV detector.
TLC：In a normal phase silica gel TLC analysis, a solvent system of chloroform-methanol-aqueous ammonia gives a relatively a good separation. NH₂-type silica gel is also effective. Dragendorff’s reagent is a selective visualizing reagent for alkaloids. Tertiary amines and quaternary ammonium salts give orange spots.

■Storage Precautions
Alkaloids are relatively stable at room temperature, however, they tend to form carbonate salts due to their basicity by reaction with carbon dioxide in the air. In addition, they are usually colorized by reaction with oxygen. Therefore, opened bottles should be stored in the refrigerator or frozen with inert gas such as nitrogen or argon.

WARNING
Some of the alkaloids may cause serious physiological actions in very minute amounts. They may cause paralysis, convulsions, and death in the worst case. To avoid inhalation and contacting with skin, wear protective goggles, mask and eyeglasses when handling. Sufficient caution should be taken, when using these compounds, from the opening to the disposal of the reagents.

Tropane Alkaloids

Piperidine Alkaloids

Phenylethylamines

Isoquinoline Alkaloids

Quinoline Alkaloids

Pyridine Alkaloids

Indole Alkaloids

Imidazole Alkaloids

Purine Alkaloids

Others

Tropane Alkaloids

A0754	A0550	B3401
E0834	H1289	H0155
H0156	H0448	H0450
H0451	H0452	H0453
N0844	S0021	S0231
S0230	S0229	T0534

A0754	Atropine
A0550	Atropine Sulfate Monohydrate
B3401	N-(tert-Butoxycarbonyl)nortropinone
E0834	N-(Ethoxycarbonyl)nortropinone
H1289	(+/-)-exo-6-Hydroxytropinone
H0155	Homatropine Hydrobromide
H0156	Homatropine Hydrochloride
H0448	Homatropine Methyl Bromide
H0450	(-)-Hyoscyamine
H0451	Hyoscyamine Hydrobromide
H0452	Hyoscyamine Hydrochloride
H0453	Hyoscyamine Sulfate Hydrate
N0844	Nortropinone Hydrochloride
S0021	Scopolamine Hydrobromide Trihydrate
S0231	Scopolamine Methyl Bromide
S0230	Scopolamine Methyl Nitrate
S0229	Scopolamine N-Oxide Hydrobromide Monohydrate
T0534	Tropine

Piperidine Alkaloids

L0096

M2120

P0460

L0096	Lobeline Hydrochloride
M2120	Matrine
P0460	Piperine

Phenylethylamines

A0172	A0173	A0175
A0909	A1234	D2104
E0387	E0381	D0651
A0305	I0261	I0260
M0844	M1891	A0906
N0389	P0395	P0396
P0397	P0398	S0232
S0233	A0302

A0172	DL-Adrenaline
A0173	L-Adrenaline
A0175	L-Adrenaline Bitartrate
A0909	DL-Adrenaline Hydrochloride
A1234	Adrenalone Hydrochloride Hydrate
D2104	2-(3,4-Dimethoxyphenyl)-N-methylethylamine
E0387	2-Ethylamino-1-(4-methoxyphenyl)propane Hydrochloride
E0381	Etilefrine Hydrochloride
D0651	Hordenine Sulfate Dihydrate
A0305	3-Hydroxytyramine Hydrochloride
I0261	Isoprenaline Sulfate Dihydrate
I0260	Isoproterenol Hydrochloride
M0844	2-(2-Methoxyphenyl)ethylamine
M1891	2-(3-Methoxyphenyl)ethylamine
A0906	L-Noradrenaline Bitartrate Monohydrate
N0389	DL-Norphenylephrine Hydrochloride
P0395	L-Phenylephrine
P0396	L-Phenylephrine Bitartrate
P0397	DL-Phenylephrine Hydrochloride
P0398	(R)-Phenylephrine Hydrochloride
S0232	Synephrine
S0233	Synephrine Tartrate
A0302	Tyramine

Isoquinoline Alkaloids

B0450	B0451	E0007
P0016	C0433

B0450	Berberine Chloride Hydrate
B0451	Berberine Sulfate Hydrate
E0007	Emetine Dihydrochloride Hydrate
P0016	Papaverine Hydrochloride
C0433	Tubocurarine Chloride Pentahydrate

Quinoline Alkaloids

B1683	B1689	B1684
B1685	C1495	C0347
C0348	C0349	C0350
C0351	C0791	H0752
I0728	Q0006	Q0010
Q0028	Q0030

B1683	N-Benzylcinchonidinium Chloride [Chiral Phase-Transfer Catalyst]
B1689	N-Benzylcinchoninium Chloride [Chiral Phase-Transfer Catalyst]
B1684	N-Benzylquinidinium Chloride [Chiral Phase-Transfer Catalyst]
B1685	N-Benzylquininium Chloride [Chiral Phase-Transfer Catalyst]
C1495	(S)-(+)-Camptothecin
C0347	Cinchonidine
C0348	Cinchonidine Dihydrochloride
C0349	Cinchonidine Sulfate Dihydrate
C0350	Cinchonine
C0351	Cinchonine Hydrochloride Hydrate
C0791	Cinchonine Sulfate Dihydrate
H0752	Hydroquinidine Hydrochloride
I0728	beta-Isocupreidine
Q0006	Quinidine
Q0010	Quinidine Sulfate Dihydrate
Q0028	Quinine
Q0030	Quinine Hydrochloride Dihydrate

Pyridine Alkaloids

A0523	N0079	N0080
N0081	T1429

A0523	Arecoline Hydrobromide
N0079	Nicotine
N0080	Nicotine Bi-L-(+)-tartrate Dihydrate
N0081	Nicotine Sulfate (40-45% in Water as Nicotine base)
T1429	Trigonelline Hydrochloride

Indole Alkaloids

B0670	B0946	B0671
B0672	C0001	D2633
D1247	D0653	H0001
H0002	P0406	P0407
R0007	S0249	S0257
S0093	S0094	V0061
Y0002

B0670	Brucine Dihydrate
B0946	Brucine Anhydrous
B0671	Brucine Hydrochloride Monohydrate
B0672	Brucine Sulfate Heptahydrate [for Nitrate Analysis]
C0001	Cacotheline Monohydrate
D2633	Dihydroergotamine Mesylate
D1247	Dihydroergotamine Tartrate
D0653	Gramine
H0001	Harmine
H0002	Harmine Hydrochloride
P0406	Physostigmine free base
P0407	Physostigmine Salicylate
R0007	Reserpine
S0249	Strychnine
S0257	Strychnine Hydrochloride Hydrate
S0093	Strychnine Nitrate
S0094	Strychnine Sulfate Pentahydrate
V0061	Vincamine
Y0002	Yohimbine Hydrochloride

Imidazole Alkaloids

H0146	H0147	P0434
P0399

H0146	Histamine Dihydrochloride
H0147	Histamine Diphosphate Hydrate
P0434	Pilocarpine Hydrochloride
P0399	Pilocarpine Nitrate

Purine Alkaloids

B3456	C2042	C1103
C0293	M1756	M2073
T0178	T0179

B3456	8-Bromotheophylline
C2042	Caffeine
C1103	1-(3-Chloropropyl)theobromine
C0293	8-Chlorotheophylline
M1756	3-Methyl-7-propylxanthine
M2073	3-Methylxanthine
T0178	Theobromine
T0179	Theophylline

Others

M1149	C0380	G0293
T0329

M1149	Capsaicin (Natural)
C0380	Colchicine (contains 5% Ethyl Acetate at maximum)
G0293	Galantamine Hydrobromide
T0329	Tomatine [for Cholesterol assay]