It was thought that the dense functionalization and various
rigidifying elements within 4 might render compounds of this
type V-ATPase inhibitors themselves.28 To test this, the V-ATPase
inhibitory activity of compounds 20, 21, and the previously
prepared C3–C13 fragment (3) was measured using a convenient
Arabidopsis-based V-ATPase assay (Scheme 5).
suggest that, like the plecomacrolides,34 macrolactone formation
is essential for archazolid V-ATPase binding and inhibition.
Conclusions
A convergent synthesis of the archazolid “western hemisphere”
has been completed that is particularly well-suited for the large-
scale preparation of advanced intermediates and access to a series
of side-chain analogues. The V-ATPase inhibitory activity of this
material was then evaluated using a tractable Arabidopsis-based V-
ATPase assay. Assay results indicate that the macrocyclic structure
of the archazolids is critical to their V-ATPase inhibitory activity.
Efforts are ongoing to complete the synthesis of the natural
product and analogues for future SAR studies using our plant-
based assay method.
Scheme 5 Synthetic western hemisphere derivatives.
Acknowledgements
Acidification of the plant vacuole by the V-ATPase facilitates
cell expansion by generating turgor pressure through solute
accumulation.29 Selective inhibition by bafilomycin A, in fact, was
a key component in identifying the first plant V-ATPase29 and it
is known that the selective inhibition of concanamycin A inhibits
Arabidopsis cell elongation in a dose dependent manner.30 The first
V-ATPase mutant identified in plants, det3, exhibits a reduction
in subunit c and in V-ATPase activity, resulting in the loss of the
etiolated (dark) growth habit in seedlings.31 A key component in
the etiolated habit is stem elongation driven by V-ATPase mediated
cell expansion. Cell growth in Arabidopsis seedlings was assayed
by measuring etiolated seedling stem length in the presence of
varying amounts of inhibitors (Fig. 3).32
Generous financial support from Western Washington Univer-
sity, M.J Murdoch Charitable Trust and Research Corporation
departmental development grant, and the Dreyfus Foundation
(fellowship to L. S.) is gratefully acknowledged.
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While the plants proved highly sensitive to the known V-
ATPase inhibitors bafilomycin A and concanamycin A, none
of the synthetic archazolid derivatives displayed any significant
V-ATPase inhibitory activity in this assay.33 This data would
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