It depends whether you intended for the real estate to be an investment, rental or if you are building your own house on it.
If it is purchased as an investment, then you can deduct it up to the amount of any investment income.
If the promissory note is used to purchase your home, then you could potential deduct it on your Schedule A as qualified mortgage interest including points (if you are the buyer).
If the note is used to purchase rental property, then you could deduct the interest incurred to produce rents or royalties (this may be limited). See
Publication 527,
Residential Rental Property.
