  We report exploratory Chandra observations of 14 high-redshift (z=4.06-5.27),
optically selected quasars. Ten of these quasars are detected, increasing the
number of z>4 X-ray detected quasars by 71%. Our detections include four of the
five highest-redshift X-ray detected quasars to date, among them SDSSp
J021043.17-001818.4, the highest-redshift (z=4.77) radio-loud quasar detected
in the X-ray band. The four undetected objects are the Broad Absorption Line
quasars SDSSp J112956.10-014212.4 and SDSSp 160501.21-011220.0, the weak
emission-line quasar SDSSp J153259.96-003944.1, and the quasar PSS 1435+3057. A
comparison of the quasars' spectral energy distributions (by means of the
optical-to-X-ray spectral index, alpha_ox) with those of lower-redshift samples
indicates that the Chandra quasars are X-ray fainter by a factor of approx 2.
X-ray faintness could be associated with the presence of large amounts of gas
in the primeval galaxies harboring these high-redshift quasars, as suggested by
recent studies conducted on z>4 quasars in other bands. Using the current
Chandra data, predictions for the next generation of X-ray observatories,
Constellation-X and Xeus, are also provided.
