Catalyzes the thiamine diphosphate-dependent decarboxylation of 2-oxoglutarate and the subsequent addition of the resulting succinic semialdehyde-thiamine pyrophosphate anion to isochorismate to yield 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylate (SEPHCHC). 2-oxoglutarate + H(+) + isochorismate = 5-enolpyruvoyl-6-hydroxy-2-succinyl-cyclohex-3-ene-1-carboxylate + CO2 Binds 1 thiamine pyrophosphate per subunit. Quinol/quinone metabolism; 1,4-dihydroxy-2-naphthoate biosynthesis; 1,4-dihydroxy-2-naphthoate from chorismate: step 2/7. Quinol/quinone metabolism; menaquinone biosynthesis. Homodimer. Was identified as a high-confidence drug target. Belongs to the TPP enzyme family. MenD subfamily.