  We report upper limits to the very high energy flux (E>100 GeV) of the flat
spectrum radio quasar 3C454.3 (z=0.859) derived by the Cherenkov telescope
MAGIC during the high states of July/August and November/December 2007. We
compare the upper limits derived in both time slots with the available
quasi-simultaneous MeV-GeV data from the AGILE gamma-ray satellite and
interpret the observational results in the context of leptonic emission models.
The source was observed with the MAGIC telescope during the active phases of
July-August 2007 and November-December 2007 and the data were analyzed with the
MAGIC standard analysis tools. For the periods around the ends of July and
November, characterized by the most complete multifrequency coverage, we
constructed the spectral energy distributions using our data together with
nearly simultaneous multifrequency (optical, UV, X-ray and GeV) data. Only
upper limits can be derived from the MAGIC data. The upper limits, once
corrected for the expected absorption by the extragalactic background light,
together with nearly simultaneous multifrequency data, allow us to constrain
the spectral energy distribution of 3C454.3. The data are consistent with the
model expectations based on the inverse Compton scattering of the ambient
photons from the broad line region by relativistic electrons, which robustly
predicts a sharp cut-off above 20-30 GeV.
