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