Alkaloids in Plant Chemistry

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Questions and Answers

Which of the following suffixes indicates isomerism in alkaloids?

-dine (correct)

-ine

-idine

-mine

What is the primary pharmacological action of Atropine?

Antihypertensive

Smooth muscle relaxant

Mydriatic (correct)

Analgesic

How are most alkaloids characterized in terms of physical properties?

Non-volatile liquids only

Amorphous solids only

Colored and volatile liquids

Crystalline solids with definite melting points (correct)

Which alkaloidal base is sparingly soluble in ether?

Morphine Signup and view all the answers

Which of the following alkaloids is classified as a central stimulant?

Strychnine Signup and view all the answers

What solubility characteristic is true about alkaloidal salts?

Soluble in water Signup and view all the answers

Which of the following correctly describes alkaloids with a high degree of unsaturation?

They may exhibit colors like yellow or red. Signup and view all the answers

Which of the following statements about the nomenclature of alkaloids is true?

Generic names can be derived from the plant source. Signup and view all the answers

Which of the following statements is true regarding pseudo alkaloids?

They are considered very weak bases. Signup and view all the answers

Which of the following alkaloids serves as an example of a true alkaloid?

Atropine Signup and view all the answers

What distinguishes alkaloids from other compounds?

They contain nitrogen in a heterocyclic ring. Signup and view all the answers

What is a common feature of all alkaloids?

They contain nitrogen. Signup and view all the answers

Which of the following is an example of a true alkaloid?

Morphine Signup and view all the answers

What ecological function do alkaloids primarily serve in plants?

They aid in detoxification and protection. Signup and view all the answers

Which alkaloid is incorrectly paired with its category?

Ephedrine - Proto alkaloid Signup and view all the answers

What is the classification of alkaloids based on their physiological activity called?

Pharmacological classification Signup and view all the answers

The prefix 'Nor-' in alkaloid nomenclature indicates what process?

N-demethylation or N-demethoxylation. Signup and view all the answers

Which alkaloid is considered a protoalkaloid?

Ephedrine Signup and view all the answers

Which compound does NOT fit the definition of being an alkaloid?

Sodium Signup and view all the answers

What is a key characteristic of true alkaloids?

They occur in plants as salts of organic acids. Signup and view all the answers

Which statement about the basicity of alkaloids is true?

Some alkaloids are amphoteric. Signup and view all the answers

Which precursor or building block is used for the biosynthesis of morphine?

Phenylalanine Signup and view all the answers

Which of the following statements about alkaloids is incorrect?

Alkaloids can be toxic. Signup and view all the answers

Which alkaloid is NOT classified as a typical alkaloid?

Colchicine Signup and view all the answers

Which reagent produces a yellow precipitate when tested with alkaloids?

Hager's reagent Signup and view all the answers

Which reagent is associated with the formation of a reddish-brown precipitate?

Wagner's reagent Signup and view all the answers

What color does p-Dimethylaminobenzaldehyde reagent produce when reacting with ergot alkaloids?

Blue Signup and view all the answers

Which reagent combines H2SO4 and ammonium molybdate?

Mandalin's reagent Signup and view all the answers

What is the nature of the false positive results seen with alkaloidal precipitants?

Alkaloidal precipitants may also react with tannins and proteins. Signup and view all the answers

Which form of alkaloids is generally more active?

Levo (-) form Signup and view all the answers

Which of the following alkaloids is active in the d-form?

(+) Tubocurarine Signup and view all the answers

What is responsible for the basicity of alkaloids?

Unshared pair of electrons on nitrogen Signup and view all the answers

Which statement about quaternary ammonium compounds is true?

They are not affected by OH- because they lack a proton. Signup and view all the answers

What affects the basicity of alkaloids according to the content?

Proximity of electron withdrawing groups to the nitrogen Signup and view all the answers

Which alkaloid is known to sublime when heated?

Caffeine Signup and view all the answers

What type of nitrogen atom does a tertiary amine in alkaloids possess?

Three organic groups Signup and view all the answers

How are the salts of alkaloids generally viewed in terms of stability?

More stable than their free bases Signup and view all the answers

What occurs when alkaloids react with dilute acids?

They form salts. Signup and view all the answers

Under drastic conditions with concentrated acids, which change may alkaloids NOT undergo?

Ethylation Signup and view all the answers

Which of the following alkaloids can undergo hydrolysis when heated with alkalis?

Atropine Signup and view all the answers

What is released when weak alkalies act on alkaloidal salts?

Alkaloidal bases Signup and view all the answers

What happens to the lactone ring of alkaloids like Pilocarpine when treated with strong bases?

The lactone ring opens. Signup and view all the answers

What is a characteristic of reagents from the first group used for detecting alkaloids?

They form amorphous or crystalline precipitates. Signup and view all the answers

What component is produced when Solanine is hydrolyzed?

Solanidine Signup and view all the answers

Which of the following is necessary for the demethoxylation of alkaloids?

Presence of methoxy groups Signup and view all the answers

Study Notes

Alkaloids

Alkaloids are basic, heterocyclic nitrogenous compounds of plant origin; they are physiologically active.
Basicity attributed to the nitrogen atom.
They have complex molecular structures and potent therapeutic effects (e.g., vincristine, atropine, morphine, quinine).
Natural plant compounds with a basic character and containing at least one nitrogen atom in a heterocyclic ring.
Possess various biological activities.
Alkaloids are cyclic compounds with nitrogen in a negative oxidation state.
Limited distribution in living organisms.

Classification

Taxonomic: Classified based on plant family (e.g., Solanaceae, Papilionaceous) or genus (e.g., Ephedra, Cinchona).
Pharmacological: Classified based on their pharmacological activity or response (e.g., analgesic alkaloids, cardio-active alkaloids). These groups don't share similar chemical properties.
Biosynthetic: Classified by the precursors or building blocks used by plants to synthesize the complex structure of alkaloids (e.g., morphine, papaverine, narcotine, tubocurarine, and calchicine are derived from phenylalanine and tyrosine).

Hagnauers System of Classification

True (Typical) Alkaloids: Basic nitrogenous compounds; toxic and exhibit a wide variety of physiological activities. Derived from amino acids with nitrogen in a heterocyclic ring. Soluble in cell sap (mostly as salts of organic acids). (e.g., Atropine).
Protoalkaloids (Biological Amines): Simple amines where the nitrogen is not in a heterocyclic ring. Derived from amino acids and possess basic characteristics. (e.g., Ephedrine, Mescaline).
Pseudo Alkaloids: Not derived from amino acid precursors but contain nitrogen in a heterocyclic ring. (e.g., Steroidal alkaloids like Solanine, purine base alkaloids like Caffeine).

Nomenclature

Prefixes:
"Nor-": Indicates N-demethylation or N-demethoxylation (e.g., norpseudoephedrine).
"Apo-": Indicates dehydration (e.g., apoatropine).
"Iso-, pseudo-, neo-, epi-": Indicate different types of isomers (e.g., ephedrine and pseudo-ephedrine, vittatine and epivittatine).
Suffixes:
"-dine": Indicates isomerism (e.g., quinine and quinidine).
"-ine": Used to show less active isolysergic acid series (e.g., ergotaminine).

Alkaloid's Properties and Function

Play a protective role due to their toxic properties (bitter taste).
End products of detoxification reactions.
Some supply energy (sugar moieties) and/or nitrogen reserves.
Regulatory effects on plant growth.
Wide range of pharmacological activities (analgesic, narcotic, stimulant, mydriatic, etc.)

Physical Characteristics

Mostly crystalline solids with a melting point.
Few are amorphous and some are liquids (volatile or non-volatile).
Most are colourless, few are coloured (complex aromatic structures).
Solubility in water varies considerably (mostly insoluble but some exceptions).
Solubility in organic solvents.
Alkaloidal salts are usually soluble in water, with varying solubilities in organic solvents.

Isomerism

Many alkaloids contain one or more asymmetric carbon atoms.
Levo (-) isomer is often more active than dextro (+).
Some exceptions exist (e.g., (+)tubocurarine).
Racemic mixture may be active.

Action of Acids and Alkalies

Alkaloids react with dilute acids to form salts.
Concentrated acids can cause significant changes.
Some alkaloids undergo dehydration, creating anhydro or apo- derivatives.
Some alkaloids containing ester linkages can be hydrolyzed.
Demethoxylation can occur from some alkaloids.
Alkaloids react with weak bases (liberating bases from their salts).
Stronger bases (e.g., Na or K hydroxide) can form salts with alkaloids containing phenolic groups, or cause hydrolysis.
Alkaloids with lactone rings can undergo ring opening reactions in the presence of alkali.

Detection of Alkaloids

Detected using specific reagents which react with alkaloids to produce precipitates or characteristic colours.
Important Note: Alkaloidal precipitants can give false positives with other plant constituents (like tannins, proteins, coumarins, and some flavonoids). Removal of these is crucial to avoid false results.

Alkaloidal Color Reagents

Give characteristic colors with most alkaloids.
Many contain sulfuric acid, and the reagents react with the alkaloids directly, not just their solutions.
Various reagents exist with different colours for differing alkaloids (e.g., Erdman's, Marquis, Mandelin's, Froehd's, Mecke's, Shaer's, and Liebermann's reagents).
Additional specific reagents exist that produce characteristic colors with certain alkaloids.

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Description

This quiz explores the fascinating world of alkaloids, basic nitrogenous compounds derived from plants. Discover their complex structures, physiological effects, and classification based on taxonomic and pharmacological criteria. Test your knowledge on the therapeutic applications and biological activities of these intriguing natural compounds.