Chemistry Reference
In-Depth Information
2.1.8 Aromatic Polyketides and Enediynes
Aromatic polyketides are rare metabolites in marine invertebrates. Naphtho-
quinone and anthraquinone derivatives were reported as echinoderm pigments
in the earlier stage of marine natural products research. The most interesting
aromatic polyketides are the pentacyclic polyketides of the halenaquinone/
halenaquinol class. Halenaquinone (
40
) was first isolated from the sponge
Xestospongia exigua
. Compounds of this class show a variety of biologic
activities, which include inhibition of tyrosine kinase (12, 19).
HO
O
SMe
O
O
OH
OH
411:
R=
R=
O
N
H
O
O
442
: R R=
O
O
440
Only two groups of enediynes have been found from marine organisms; name-
namicin (
41
) was first isolated the Fijian tunicate
Polysyncraton lithostrotum
,
whereas shishijimicins A (
42
)-C,
-carboline-contining enediynes, were isolated
from the Japanese tunicate
Didemnum proliferum
, along with
41
, which thus
suggests the involvement of symbiotic microorganisms in their production (1).
As expected, these compounds inhibited growth of tumor cells at pM levels.
β
2.2 NONRIBOSOMAL PEPTIDES AND AMINO ACID DERIVATIVES
In addition to ribosomal peptides, some of which exhibit interesting bioactivities
as is the case of conotoxins, marine organisms; in particular, sponges and tuni-
cates contain a wide variety of nonribosomal peptides, many of which contain
unusual or unprecedented amino acids. It should be noted that these peptides
show a range of biological activities.
2.2.1 Amino Acid Derivatives
Microalgae and macroalgae often contain UV-absorbing amino acids collectively
dubbed “mycosporines”. Mycosporine-glycine (
43
) is most widely distributed in
marine organisms that use it for protection from UV irradiation. Domoic acid
(
44
) is not only a helminthic agent originally isolated from a red alga, but also it
is a causative agent of amnesic shellfish poisoning (14). It is a potent agonist of
glutamate receptors. Dysiherbaine (
45
), which is a novel betaine isolated from
the sponge
Dysidea herbacea
, is a potent non-MNDA-type agonist with very
high affinity for kainate receptors (20).
