We don't have synonyms for of interest yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are by interest, low interest and ex interest.
(n) :
a great attention and concern from someone or something; the price paid for obtaining, or price received for providing, money or goods in a credittransaction, calculated as a fraction of the amount or value of what was borrowed
(n) :
a great attention and concern from someone or something; the price paid for obtaining, or price received for providing, money or goods in a credittransaction, calculated as a fraction of the amount or value of what was borrowed