OIA2007 ALKALOIDS

Alkaloids

Naturally occurring basic compounds containing nitrogen, usually in heterocyclic rings; mostly derived from amino acids.

Functions in nature

Defense (toxic/bitter), nitrogen and energy storage, growth regulators, neurotransmitter roles, and metabolic waste products.

Alkaloid nomenclature

Ends in “-ine”; may reflect plant genus (atropine), species (cocaine), discoverer (pelletierine), or effect (emetine).

True alkaloids

Have nitrogen in a heterocyclic ring and are derived from amino acids (e.g., morphine, nicotine, atropine).

Protoalkaloids

Nitrogen not in a ring but still derived from amino acids (e.g., ephedrine, mescaline).

Pseudoalkaloids

Have nitrogen in a ring but not from amino acids (e.g., caffeine, theobromine); obtain nitrogen via transamination.

Physical forms

Most are crystalline solids; some are amorphous (emetine), volatile liquids (nicotine), or non-volatile liquids (pilocarpine).

Solubility

Alkaloidal bases = soluble in alcohol & organic solvents, poorly in water.

Salts = soluble in water.

Water-soluble bases

Caffeine, ephedrine, codeine, colchicine, pilocarpine, quaternary ammonium compounds.

Alkaloid extraction method

Use lime (Ca(OH)₂) to convert alkaloid salts to free base (soluble in organic solvents), then use acid to re-form salts.

Acids in extraction

HCl, H₂SO₄, tartaric acid → convert free alkaloids to water-soluble salt forms.

Alkaloid detection reagents

Mayer’s (cream ppt), Wagner’s (reddish-brown ppt), Dragendorff’s (reddish-brown ppt), Hager’s (yellow ppt).

Main biosynthetic precursors

Amino acids (tyrosine, tryptophan, lysine, ornithine), purines, terpenes.

Caffeine biosynthesis

Derived from purine pathway.

Alkaloid classification by skeleton

Can also be based on ring type and carbon framework.

Caffeine (Coffee)

From Coffea arabica; CNS stimulant.

Theobromine (Cocoa)

From Theobroma cacao; diuretic and smooth muscle relaxant.

Theophylline (Tea)

From Camellia sinensis; smooth muscle relaxant (esp. bronchi).

Adenine (Tea)

Minor purine alkaloid.

Trigonelline (Coffee)

Another minor component with metabolic effects.

Reserpine (Rauvolfia serpentina)

Antihypertensive, sedative, tranquilizer.

Yohimbine (Rauvolfia)

Aphrodisiac and hypotensive; CNS active.

Vinblastine/Vincristine (Catharanthus roseus)

Anticancer drugs; inhibit microtubule formation.

Ergot alkaloids (Claviceps purpurea)

Ergotamine (migraine), Ergonovine (oxytocic), Ergotoxine (vasoconstrictive).

Mitragynine (Mitragyna speciosa, "Kratom")

Stimulant and analgesic; acts on opioid receptors.

Quinine (Cinchona spp.)

Antimalarial agent, especially for Plasmodium species.

Quinidine (Cinchona spp.)

Used as an antiarrhythmic.

Cinchonidine / Cinchonicine

Anti-inflammatory actions.

Morphine (Opium poppy)

Narcotic analgesic; strong CNS depressant.

Codeine

Antitussive and mild analgesic; derived from morphine (methylated) or thebaine (reduction & demethylation of morphine).

Noscapine (Narcotine)

Non-narcotic; antitussive.

Papaverine

Smooth muscle relaxant; vasodilator.

Thebaine

Opioid precursor; less active, but base for semi-synthetic drugs.

Heroin

Diacetylmorphine; synthesized from morphine (acetylated), highly addictive.

Atropine (Atropa belladonna)

Anticholinergic; used for bradycardia, mydriasis, antidote for organophosphate poisoning.

Hyoscyamine

Antispasmodic; enantiomer of atropine.

Scopolamine (Hyoscine)

Antiemetic (motion sickness), sedative.

Nicotine (Pyrrolidine/Pyridine type)

Highly addictive stimulant from Nicotiana tabacum.

Pyrrolizidine alkaloids

Toxic; found in some herbal products; hepatotoxic and carcinogenic.

Amine alkaloids

Lack a heterocyclic ring; simpler structure (e.g., ephedrine).