ALKALOIDS Questions :

ALKALOIDS Questions :

Select the true statement& .

A.Caffine, a pseudo-alkaloid: Water INsoluble & Gives negative standard qualitative test of true alkaloids

B.Caffine, a pseudo-alkaloid: Water soluble & Gives positive standard qualitative test of true alkaloids

C.Homatropine , a pseudo-alkaloid: Ether soluble & Gives negative standard qualitative test of true alkaloids

D.Colchicine, a pseudo-alkaloid: Not soluble in both ether & water

ANS:B

A-->false R1:Caffeine is WATER SOLUBLE.R2:Gives positive qualitative test of true alkaloids.

C-->false R1:Homatropine is TRUE alkaloid.R2:Gives positive std qualitative test for true alkaloids.

D-->false R1:Colchicine is PROTO ALKALOID/AMINO ALKALOID.R2:It is highly soluble in H20,ALKALINEH20,ACID.

STATEMENTS:

S1:TRUE alkaloids are toxic, N--> INSIDE ring, Always basic in nature:Salts of organic acid.

S2:PROTO ALKALOIDS/AMINOALKALOIDS,N-->Outside ring,Simple amines.Eg:MESCALINE,N,N-dimethyl tryptamine,@@colchicine,ephedrine.

S3:PSEUDO ALKALOIDS-->STP-->Steroidal,@@Terpenoidal,Purines--->Give std qualitative tests for alkaloids.conessine,caffeine.

Precursors---------> Alkaloids Included:

1.Ornithine, putrescine, proline-----> Pyrrole, pyrrolizidine, tropane.

2.Lysine ------> Pyridine, norlupinane.

3.Tyrosine, phenylalanine----->Protoalkaloids

4.Tyrosine, phenylalanine----->Isoquinoline.@@@@@

4.Tryptophan, tryptamine---->Quinoline, indole.

5.Histidine, threonine----->Imidazole.

6.Adenine, purine, xanthine, hypoxanthine------>Purine.

7.Acetate or mevalonic acid------>Steroidal and terpenoid pseudoalkaloids.

S1:1,2,4,5

S2:3.

S3:7,6.

ALKALOIDS:

Pseudoalkaloids are terpenoids that contain nitrogen or are derived from acetate, such as CONIINE.

Protoalkaloids contain an amine structure but not within a heterocyclic ring, such as EPHEDRINE.

The chemical and biological properties of Pseudoalkaloids and Protoalkaloids are sufficiently similar to those of Heterocyclic alkaloid that they are included in this category.

###S:All the 3 types of alkaloids gives positive standard qualitative tests for alkaloids.

The nitrogen in alkaloids generally acts as a weak base, although this varies according to other functional groups and the exact configuration of the alkaloids.

Primary, secondary, and tertiary amines (the nitrogen connected to one, two, or three carbons, respectively), as well as saturated, heterocyclic amines, are the most basic alkaloids.

[R-NH2]Primary:MESCALINE---->PROTO/AMINO ALKALOID.

[R2-NH]Secondary:EPHEDRINE--->PRORO/AMINO ALKALOID.

[R3-NH]Tertiary:ATROPINE---->TRUE ALKALOID.

S1:Primary amine & Secondary amine containing alkaloids are PROTO ALKALOIDS.

s2:Tertiary alkaloids are TRUE ALKALOIDS.

@@@@ Aromatic and ANILINE heterocyclic amines are slightly basic.

@@Amides and quaternary amines are NEUTRAL, and PHENOLICS are actually ACIDIC.

DECREASING ORDER OF BASIC nature :ANILINE>AMIDES>PHENOLIC.

Alkaloids, particularly amines and other basic alkaloids, are usually found as salts in plants.

They remain in salt form when placed in an acidic solution, and any free alkaloid generally becomes salt.

This is critical because the salt forms are water soluble and the free alkaloids generally are not.

@@@For example, free quinine is 0.1% water soluble, and quinine hydrochloride is 99% water soluble.

@@@Acidic and neutral free alkaloids, such as caffeine, tend to be hydrophilic and may not form salts.

Alkaloids are variably bioavailable.

They tend to be oxidized by the cytochrome P450 system to form@@@@ N-oxide compounds, which are water soluble and NONtoxic.

The N-oxides can be reduced in the body to their parent alkaloids and may cause problems or bring benefits.

@@@@@Alkaloids are irreversibly bound and are precipitated by TANNINS, making them almost totally unabsorbable.

@@@@The two should generally be kept separate to avoid this interaction, although TANNINS can also serve as a useful immediate treatment for acute alkaloid overdose.

Alkaloids generally have a strong bitter taste.

They tend to act as @@@ digestive stimulants, as was previously discussed with SESQUITERPENE LACTONES and IRIDOID GLYCOSIDES.

Otherwise, they have extremely diverse clinical properties.

Several examples are given here to illustrate this diversity.

The only rule that is generally true and inherent to the definition of these compounds is that they tend to be POTENT, meaning that small doses are all that are necessary to produce significant effects.

@@@@Atropine [a racemic mixture of (-)- and (+)-hyoscyamine] and scopolamine are tropane alkaloids found in Atropa belladonna (belladonna), Datura spp (thornapple), and Hyoscyamus niger (henbane).

@@@@@These alkaloids are muscarinic receptor antagonists that give these herbs strong anticholinergic activity.

They are used to treat smooth muscle spasm, hypersecretion, and pain.

Pyrrolizidine alkaloids (PA) have no clear therapeutic benefit (although at least one, indicine N-oxide, is being studied as an anticancer agent) but are important for their potential toxicity.

Actually, only unsatured PA are toxic, and only those structures that are converted, in this case, to more toxic N-oxide forms by hepatic cytochrome P450 enzymes.

Thus, although most members of the Asteraceae and Boraginaceae families (and a few other scattered members of various other families) contain pyrrolizidine alkaloids, only a small number definitely contain the unsaturated type that may cause concern.

Because these alkaloids do not cause widespread hepatic necrosis (except when extraordinary doses are ingested), monitoring of serum liver enzymes is not an effective screening test.

@@@It should also be noted that because unsaturated pyrrolizidine alkaloids readily induce fibrosis, the damage that they cause is cumulative.

Different animal species show wide variation in susceptibility to induction of cirrhosis, hepatic venoocclusive disease, and cancer because of unsaturated PA ingestion (Unsaturated Pyrrolizidine Alkaloid-Containing Medicinal Herbs).

Even though horses and cows are said to be highly susceptible, Symphytum officinale (comfrey) leaf has been safely and effectively used as fodder for these animals in large quantities, possibly because of low unsaturated pyrrolizidine alkaloids levels in the feed.

Differences in susceptibility may result from differences in gut flora, differences in hepatic conversion, differences in hepatic glutathione production, and differences in doses ingested.

If unsaturated PA-containing herbs are to be used medicinally or as food, it is recommended that alkaline aqueous, glycerin, or dilute ethanol (<30%) extracts be prepared from aerial parts.

This method generally reduces the amount of pyrrolizidine alkaloids extracted.

Also, many supplement companies now provide extracts that are made from strains bred to contain low PA levels, or that have documented low pyrrolizidine alkaloids levels caused by extraction methods.