Alaska Stat. § 34.20.140
Where the payment of an existing contract (a bill of exchange, promissory note, bond, or other evidence of indebtedness) is secured by an instrument creating a lien upon real estate, payment on the contract does not extend the lien beyond its original or extended period as against subsequent purchasers, optionees, mortgagees, creditors, or persons acquiring a lien upon the real estate, unless