SQLAlchemy add calculated column

Using SQLAlchemy ORM I would like to add a calculated column and then sort by that column. The calculated column is the max value of two other columns (I'm trying to find the most recent interaction between 2 contacts and they can interact either through 'email' or 'notes').

I've constructed a case when statement that correctly returns the most recent interaction:

calculatedLastInteraction = case([
            (
                (organization_note.time == None) & (contact.last_interaction_time_email != None),
                contact.last_interaction_time_email
            ),
            (
                (contact.last_interaction_time_email == None) & (organization_note.time != None),
                organization_note.time
            ),
            (
                contact.last_interaction_time_email >= organization_note.time, 
                contact.last_interaction_time_email
            ),
            (
                organization_note.time > contact.last_interaction_time_email,
                organization_note.time
            )
        ],
        else_ = None).label('calculatedLastInteractionDate')

How do I add this column to an existing SQLAlchemy query?