The present invention relates to novel compounds of formula (I) or formula (Ia);or;pharmaceutically-acceptable salts, hydrates, solvates, or stereoisomers thereof, and pharmaceutical compositions of these compounds which are useful for preventive and therapeutic use in human and veterinary medicine.本發明係關於式(I)或式(Ia)之新穎化合物;或;其醫藥上可接受之鹽、水合物、溶劑合物或立體異構物,及該等化合物之醫藥組合物,其可用於人類及家畜醫學中之預防性及治療性用途。