Marine natural products (MNPs) containing pyrone rings have been isolated
from numerous marine organisms, and also produced by marine fungi and bacteria, particularly,
actinomycetes. They constitute a versatile structure unit of bioactive natural
products that exhibit various biological activities such as antibiotic, antifungal, cytotoxic,
neurotoxic, phytotoxic and anti-tyrosinase. The two structure isomers of pyrone ring are γ-
pyrone and α-pyrone. In terms of chemical motif, γ-pyrone is the vinologous form of α-
pyrone which possesses a lactone ring. Actinomycete bacteria are responsible for the production
of several α-pyrone compounds such as elijopyrones A-D, salinipyrones and violapyrones
etc. to name a few. A class of pyrone metabolites, polypropionates which have
fascinating carbon skeleton, is primarily produced by marine molluscs. Interestingly, some
of the pyrone polytketides which are found in cone snails are actually synthesized by actinomycete bacteria.
Several pyrone derivatives have been obtained from marine fungi such as Aspergillums flavus, Altenaria sp.,
etc. The γ-pyrone derivative namely, kojic acid obtained from Aspergillus fungus has high commercial demand
and finds various applications. Kojic acid and its derivative displayed inhibition of tyrosinase activity and, it is
also extensively used as a ligand in coordination chemistry. Owing to their commercial and biological significance,
the synthesis of pyrone containing compounds has been given attention over the past years. Few reviews
on the total synthesis of pyrone containing natural products namely, polypropionate metabolites have been reported.
However, these reviews skipped other marine pyrone metabolites and also omitted discussion on isolation
and detailed biological activities. This review presents a brief account of the isolation of marine metabolites
containing a pyrone ring and their reported bio-activities. Further, the review covers the synthesis of marine
pyrone metabolites such as cyercene-A, placidenes, onchitriol-I, onchitriol-II, crispatene, photodeoxytrichidione,
(-) membrenone-C, lihualide-B, macrocyclic enol ethers and auripyrones-A & B.
Marine Natural Products from Tunicates and Their Associated Microbes
