At a minimum, it shows bad judgment for an insider to buy shares while an acquisition is in late-stage discussions; at worst, it shows recklessness.
Note that buying shares on the open market while possessing material non-public information (what RTRX’s CEO did) is completely different from exercising options while possessing material non-public information (what ENTA’s CEO and CSO did). The former is a violation of securities laws, while the latter isn’t.