Easy enough in VBA by manipulating the range. With the cursor in the word you wish to keep i.e. alimentary run the following

Sub Macro1()
'Graham Mayor - https://www.gmayor.com - Last updated - 02 Jul 2021 
Dim oRng As Range
    Set oRng = Selection.Words(1) 'set a range to the word that contains the cursor
    With oRng
        .Characters(1).Case = wdUpperCase 'make the first character of that word upper case
        .Collapse 1 'collapse the range to its start
        .MoveStartUntil Chr(46), wdBackward 'move the start to the previous full stop/period
        .MoveStartWhile Chr(32) 'move back to retain the space after the full stop/period
        .Text = "" 'clear the range
    End With
    Set oRng = Nothing
End Sub