  Interstellar chemistry in low metallicity environments is crucial to
understand chemical processes in the past metal-poor universe. Recent studies
of interstellar molecules in nearby low-metallicity galaxies have suggested
that the metallicity has a significant effect on chemistry of star-forming
cores. Here we report the first detection of a hot molecular core in the
extreme outer Galaxy, which is an excellent laboratory to study star formation
and interstellar medium in a Galactic low-metallicity environment. The target
star-forming region, WB89-789, is located at the galactocentric distance of 19
kpc. Our ALMA observations in 241-246, 256-261, 337-341, and 349-353 GHz have
detected a variety of carbon-, oxygen-, nitrogen-, sulfur-, and silicon-bearing
species, including complex organic molecules (COMs) containing up to nine
atoms, towards a warm (>100 K) and compact (<0.03 pc) region associated with a
protostar (~8x10^3 L_sun). Deuterated species such as HDO, HDCO, D2CO, and
CH2DOH are also detected. A comparison of fractional abundances of COMs
relative to CH3OH between the outer Galactic hot core and an inner Galactic
counterpart shows a remarkable similarity. On the other hand, the molecular
abundances in the present source do not resemble those of low-metallicity hot
cores in the Large Magellanic Cloud. The results suggest that a great molecular
complexity exists even in a primordial environment of the extreme outer Galaxy.
The detection of another embedded protostar associated with high-velocity SiO
outflows is also reported.
