TBR Biology Section VII confusion: Oxalosuccinate (TCA metabolite) - alpha or beta keto acid?

[matchmeifyoucan]

The TL;DR version is in bold. Thanks!

ISSUE 1: According to the TBR Biology part 2 book (section 7 - Metabolic Pathways; p. 195 in the newest edition - copyrighted 2016), oxalosuccinate is a beta-keto acid. In fact, the TBR book doesn't even call it oxalosuccinate (or oxalosuccinic acid); they simply refer to the metabolite as "β-Keto acid". I thought it was an α-Keto acid. Is this a mistype?

Below is the Kreb cycle metabolite oxalosuccinate (though TBR depicted a fully unprotonated version in the book; I'm not sure if that makes any difference to the issues I have below). It looks like an alpha-keto acid. If it's actually not one, can someone explain or maybe pull up a picture/diagram that will clearly show how that is? I thought I knew the difference between the alpha and beta-keto acid forms. I guess not. Oxalosuccinate escapes me.

ISSUE 2: Upon further research (i.e. a 10-minute google search), I have noticed some inconsistent data. Some sources referred to oxalosuccinate as a β-keto acid while others (the majority, it seemed) referred to it as an α-keto acid. I would love some clarity on this.

ISSUE 3 : TBR explains that oxalosuccinate is unstable because of its beta-keto form, which results in a spontaneous decarboxylation. How, Sway? (And then proceeds to use a simple/generic chemical structure of a beta-keto acid - not oxalosuccinate itself, which, to me, does not resemble the generic beta-keto acid structure - to explain the decarboxylation mechanism 😕).

ISSUE 4: I'm having trouble understanding how an alpha-keto acid, in general, is more stable than a beta-keto acid. I'm thinking that the carbonyl groups being closer in proximity in an alpha-keto acid would make an alpha-keto acid less stable than a beta-keto acid. Please help me understand what I'm missing/getting wrong.

If anyone can shine some light into any of these issues, I would greatly appreciate it. One piece of information might jog my memory. 🙂

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[aldol16]

It's both an alpha keto acid and a beta keto acid. Look at the molecule you drew. The carbonyl is alpha to the carboxylic acid on the right. It is beta to the carboxylic acid on the left. It's this second property that makes it unstable. Draw out the mechanism of decarboxylation to see why beta keto acids can decarboxylate easily whereas alpha keto acids cannot.

 

[matchmeifyoucan]

Answered succinctly. Thank you! I can't believe I was stumped on this for hours. Actually, I do. My brain was mush.

It's both an alpha keto acid and a beta keto acid. Look at the molecule you drew. The carbonyl is alpha to the carboxylic acid on the right. It is beta to the carboxylic acid on the left. It's this second property that makes it unstable. Draw out the mechanism of decarboxylation to see why beta keto acids can decarboxylate easily whereas alpha keto acids cannot.