Question: what was the date of that transaction?
SQL: SELECT T3.date_of_transaction FROM LOTS AS T1 JOIN TRANSACTIONS_LOTS AS T2 ON  T1.lot_id   =   T2.transaction_id JOIN TRANSACTIONS AS T3 ON T2.transaction_id   =   T3.transaction_id WHERE T3.share_count  >  100 AND T3.transaction_type_code   =   "PUR" ORDER BY T3.amount_of_transaction DESC LIMIT 1