How to proceed in petition/request/purchase scenario?

Hi, I want to ask a petition/request/purchase scenario. The case is as follows:
I create a purchase requesition for three items (A, B and C) continue wf until the purchase requests are generated.
At this time of these 3 items I just want to buy 2 (A and B) and C (Reject) eliminating the request.
The next step I create a purchase from the purchase request of the items A and B, and at the time of processing the purchase this item C (which had eliminated your purchase request) generates another purchase request again.

How should I proceed so that in this scenario the purchase request for item C will not be recreated?

Thanks in advance!

You should create a purchase for item C and cancel it.
This will trigger the exception on the purchase request allowing you to recreate the purchase or ignore it.