## Core Concept
The biosynthesis of purines involves the assembly of the purine ring from several precursors. The nitrogen atoms in purines are derived from specific amino acids and other nitrogen-containing molecules.

## Why the Correct Answer is Right
The purine ring is synthesized from **aspartate**, **glutamine**, and **glycine**, along with **carbon dioxide** and **formate**. The nitrogen atoms in purines are specifically contributed by aspartate and glutamine.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is actually correct in the context of providing nitrogen for purine synthesis; however, we need to verify if it's listed as the correct answer or not. Assuming it's not the correct answer based on the prompt.
* **Option B:** Similarly, if listed as incorrect, it implies contribution to purine nitrogen.
* **Option C:** If listed as incorrect, then like A and B, it contributes to nitrogen in purines.
* **Option D:** This is stated as the correct answer, implying it does not contribute nitrogen to purines.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **glycine** contributes both carbon and nitrogen to the purine ring but through different parts of its molecule.

## Correct Answer: D. Asparagine.