Abstract:
Studies towards the total synthesis of (-)-gymnodimine (1), a marine neurotoxin
with a unique molecular architecture and pronounced biological activity, are described.
These studies resulted in a convergent approach to the advanced intermediate 315,
containing the C3-C32 section of 1.
Two synthetic routes were developed to construct the tetrahydrofuran subunit of
(-)-gymnodimine. Both routes employed a highly stereoselective iodoetherification of
alkenes 120 (initial route) and 158 (second generation route) to furnish cis-2,5-
disubstituted tetrahydrofurans 121 and 159, respectively. The longest sequence in the
second generation route required 16 linear steps to the tetrahydrofuran subunits. The
initial approach needed 21 steps.
Two cyclohexene subunits of (-)-gymnodimine, 246 and 265, were prepared from
the Diels-Alder cycloadducts 213 and 214, respectively. The quaternary stereogenic
center at C22 (gymnodimine numbering) of 236 was generated by the intramolecular
lactonization of 235, which was obtained from 213.
Assembly of two subunits, 146 and 299, employing a B-alkyl Suzuki-Miyaura
reaction provided the coupled product 310 in good yield. After 310 was converted to the
terminal alkyne 313, methylation of 313 was accomplished via a Stille reaction. In
addition, a model study of the formation of the cyclic imine moiety of (-)-gymnodimine
was carried out.
