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In turn, most of the 1-substituted 2-aminoimidazole alkaloids (Figure 1.9.2) have been<br />

isolated from the Calcarea group of the genera Leucetta and Clathrina from the Red<br />

Sea and the Indo-Pacific regions. 82<br />

N<br />

H2N N<br />

Me<br />

HO<br />

OH<br />

Naamine A (7)<br />

OMe<br />

OMe<br />

OMe<br />

N<br />

H2N N O OMe<br />

Me<br />

Calcaridine A (9)<br />

N<br />

OH<br />

H2N N<br />

OMe<br />

Me<br />

Kealiinine A (11)<br />

H 2N<br />

N<br />

N<br />

OH<br />

Isonaamine A (8)<br />

N<br />

H2N N<br />

Me O<br />

O<br />

O<br />

OH<br />

O<br />

Leucettamine A (10)<br />

N<br />

H2N N<br />

Me O<br />

O<br />

Preclathridine A (12)<br />

Fig.1.9.2 Some representative 1-substituted 2-aminoimidazoles from<br />

marine sponges.<br />

Both classes of 1-substituted and 1-unsubstituted 2-aminoimidazoles possess<br />

interesting biological properties. Due to their high cytotoxicity many polysubstituted<br />

2-aminoimidazole alkaloids are involved in chemical defense of marine sponges<br />

against predators, in the prevention of the settlement of fouling and pathogenic<br />

microorganisms or in the suppression of epibiotic bacteria and spatial competition.

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