The Blues acquired Shattenkirk from the Colorado Avalanche in a trade centered around defenseman Erik Johnson, who was the No. 1 pick by St. Louis in the 2006 draft. Shattenkirk was a popular player in the Blues' locker room and one of four alternate captains.
Shattenkirk has 42 points (11 goals, 31 assists) in 61 games this season. He had 258 points (59 goals, 199 assists) in 425 NHL regular-season games in seven seasons with St. Louis.
"It's not the part of the business that you like," Pietrangelo said. "It's tough. It's always tough to see your friends go, tough to see a player of that caliber go, but it's the business and we've got to move on. ... Any time stuff like that happens, he's going to be a friend, he's going to be a friend for a long time.
"Obviously we know the [NHL Trade Deadline] is right now and it's tough for [Shattenkirk] to go through that, but it's obviously a big relief, I'm sure, for him to kind of put this in the past and move on."
With the Blues up against the NHL salary cap and with not much room for flexibility, Armstrong felt acquiring assets instead of gambling on losing another free agent was his best option.
"The highest return still was coming from a sign-and-trade," Armstrong said. "We worked out a package that we felt we were very comfortable with on a sign-and-trade and took that to Kevin and his representative. They talked to a team, couldn't find common ground, so that was null and void.
"I talked to the teams. As a team, you value your players maybe differently than they're valued around the League, on a positive and negative format. We looked out there, we told the teams that might have interest in Kevin as a rental player what we were looking for, then we went to work."
Sanford, 22, was expected to arrive in St. Louis Tuesday and was a player the Blues coveted.