2-AMINOPYRAZOLO[1,5-A]PYRIMIDINES AS POTENT AND SELECTIVE INHIBITORS OF JAK2 3IOK TRANSFERASE, KINASE, INHIBITOR, JAK2, JANUS KINASE, ATP-BINDING, CHROMOSOMAL REARRANGEMENT, DISEASE MUTATION, MEMBRANE, NUCLEOTIDE-BINDING, PHOSPHOPROTEIN, POLYMORPHISM, PROTO- ONCOGENE, SH2 DOMAIN, TYROSINE-PROTEIN KINASE