  We present the results from exploratory Chandra observations of nine high-z
(z=4.1-4.5) optically selected quasars. These quasars, taken from the DPOSS,
are among the optically most luminous z>4 quasars known (M_B=-28.4 to -30.2).
All have been detected by Chandra in exposure times of 5-6 ks, tripling the
number of highly luminous quasars with X-ray detections at z>4. These quasars'
average broad-band SEDs are characterized by steeper aox values
(<aox>=-1.81+/-0.03) than those of lower-luminosity, lower-redshift samples of
quasars. We confirm the presence of a significant correlation between the UV
magnitude and soft X-ray flux previously found for z>4 quasars. The joint 2-30
keV rest-frame X-ray spectrum of the nine quasars is well parameterized by a
simple power-law model with Gamma=2.0+/-0.2, consistent with those of lower-z
quasars. No evidence for significant amounts of intrinsic absorption has been
found (N_H<8.8x10^21 cm^-2 at 90% confidence). In general, our results show
that z=4.1-4.5 quasars and local quasars have reasonably similar X-ray and
broad-band spectra (once luminosity effects are taken into account), suggesting
that the accretion mechanisms in these objects are similar. We also present
optical spectra for these quasars obtained with the HET; this is the first time
optical spectra have been published for seven of these objects. The objects
presented in this paper are among the best z>4 targets for X-ray spectroscopy
with XMM-Newton and next-generation large-area X-ray telescopes. These will
detect or constrain FeK_alpha emission lines down to rest-frame EWs of about 50
eV and intrinsic column densities down to N_H=a few x 10^21 cm^-2 at z=4. We
also present 45 new ROSAT upper limits for z>4 quasars and a likely (3sigma)
HRI detection of the blazar GB 1713+2148 at z=4.01.
