Sesquiterpene pyridine alkaloids

Compounds belonging to this group of alkaloids are sourced from the Celas-traceae and Hippocrateaceae families and contain the sesquiterpene nucleus. More than 220 alkaloids are known in this group58. Sesquiterpene pyridine

3 * malonyl-CoA

Claisen reaction neophilic addition dehydration and enolization
1,3-dihydroxy-N-methylacridone
Pyridine Drugs

Figure 60. Structural development of acridone alkaloids.

Figure 60. Structural development of acridone alkaloids.

alkaloids can be divided into several types, such as evoninate, wilfordate, edulinate, cassinate, lower molecular weight sesquiterpene pyridine and non celastraceous sesquiterpene pyridine alkaloids58. Evoninate sesquiterpene alkaloids can again be divided into evoninate, isoevoninate, hydroxyisoevoninate, epimeric evoninate and norevoninate compounds. Evoninate sesquiterpene alkaloids are compounds in which evonic acid esterifies the sesquiterpene nucleus. Typical alkaloids of this sub-group are evonimol derivatives (e.g., evonine), euonyminol derivatives (e.g., euonymine and hippocrateine), isoeuonyminol derivatives (e.g., emarginatine), 4-Deoxysesquiterpene cores (e.g., chuchuhua-nine), cathedulin alkaloids (e.g., cathedulin), dimacrocyclic sesquiterpene pyri-dine alkaloids (e.g., triptonine). A typical isoevoninate sesquiterpene alkaloid

L-ornithine

NADPH

Nicotinic acid co2h

Nicotinic acid

NADPH

Putrescine co2h

Images Pyridine Alkaloid

Putrescine

N Nicotine

1,2-dihydropyridine

N Nicotine u N HH

1,2-dihydropyridine

Non-enzymic decomposition

NADPH

Figure 61. Structural development of pyridine alkaloids.

Nornicotine

Figure 61. Structural development of pyridine alkaloids.

is hippocrateine, and a typical hydroxyisoevoninate one is hypoglaunine. Acanthothamine is a representative compound of epimeric evoninate alkaloid. Norevoninate alkaloid has only been isolated from Hippocratea excelsa58.

Wilfordate alkaloids are another type of sesquiterpene pyridine compound. They are sesquiterpenes, macrocyclic compounds esterified by wildorfic acid. Wilforine is an example of this kind of alkaloid. Edulinate sesquiterpene pyridine alkaloids are sesquiterpene compounds esterified by edulinic acid. Cathedulin is one example. The cassinate group of sesquiterpene alkaloids contains orthosphe-nine and cassinine. These alkaloids have dihydroagarofuran sesquiterpenes ester-ified by cassinic acid. Lower-molecular-weight sesquiterpene pyridine alkaloids have only been isolated from plants of the Celastraceae family, and are characterized by the absence of a macrocyclic ring. They have a sesquiterpene core and a nitrogenous base through esterification. Lower-molecular-weight sesquiterpene pyridine alkaloids are also known as nocotinoyl sesquiterpene alkaloids58.

Non-celastraceous sesquiterpene pyridine alkaloids are those compounds which have been isolated from other plants not belonging to the Celestraceae family. Rotundine, for example, has been isolated from Cyperus rotun-dus (Cypraceae). This is a structurally interesting alkaloid because it has a sesquiterpene skeleton containing a cyclopentane ring attached to the pyridine ring58.

Natural sesquiterpene pyridine alkaloid formation needs two precursors, one for the pyridinium moiety and another for the sesquiterpene moiety. The a for formation of the pyridinium moiety is nicotinic acid, which reacts with isoleucine and, by oxidative reaction, produces evoninic acid, wilfordic acid or edulinic acids. a for the sesquiterpene moiety is still open to question, but E, E-famesyl cation has been suggested as one possibility and hedycarylol as a second. This moiety is dihydroagarofuran. Therefore, a for the sesquiterpene pyridine alkaloids is nicotinic acid and E, E-famesyl cation and, controversially, hedycaryol. The ft is amacrocycling ring formation substance (two moieties), from which the alkaloid forms (Figure 62).

The sesquiterpene pyridine alkaloids have antifeedant and insecticidal activities. Some alkaloids, such as triptonine B, hypoglaunine B, hyponine B and wilfortrine, have antivirus activity potential. Others, such as emarginatines A-B, E-G and emarginatine, have cytotoxic activity. Ebenifoline and cangorinine have immunosuppressive activity.

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