Indolizidine alkaloids

Indolizidine alkaloids contain the indolizidine nucleus with two different cycles. The structural development of this kind of alkaloid is presented in Figure 53.

co2h

co2h co2h co2h

CU^NH2

O a-aminoadipic ¿-semialdehyde

L-lysine

HSCo

Acetyl-CoA

1-indolizidinone

L-pipecolic acid

1-indolizidinone

Figure 53. Structural development of indolizidine alkaloids.

ho nn A Castanospermine Swansonine A

Figure 53. Structural development of indolizidine alkaloids.

The a is L-lysine, as in the case of piperidine, but the ft is different. The ft is a-aminoadipic acid S-semialdehyde. The ^ is L-pipecolic acid, which is synthesized in plants from piperideine-6-carboxylic acid. In the case of many other organisms, the obligatory intermedia is derived from the ft. The ^ retains one ring structure. The indolizidine nucleus will be formed only in the synthesis of the x. The deep structural change occurs when ^ is transformed by a chain of reactions: the formation of CoA ester (CoAe), the Claisen reaction with acetyl or malonyl CoA (Cra/mCoA) and the ring closure process (by amide or imine) to 1-indolizidinone, which is the x. The second obligatory intermedia (x) only has the indolizidine nucleus.

The x is transformed by hydroxylation to A, which is castanospermine. The A is a typical sub-way product. The main pathway is transformed to the x by hydroxylation and the ring fusion to another A, which is swansonine.

Both alkaloids (castanospermine and swansonine) have the ability to inhibit glycosidase enzymes (GE), the activity of which is necessary in glycoprotein biosynthesis.

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