Formula (5a): the methyl ester analog (PubChem CID 86711696) vs. 2-[(2-hydroxy-4,5-dimethoxybenzoyl)amino]-1,3-thiazole-4-carboxylic acid ethyl ester (prior art D1/D2, PubChem CID 15508009, 'Acotiamide Impurity J'): POSSIBLE_ESTER_ETHER_DERIVATIVE under Section 3(d)

Molecular weights are close (known=352.1, new=338.1) but structures differ beyond simple salt/isomer relationship -- consistent with an ester/ether/other simple derivative under Section 3(d), but NOT confirmed by substructure matching here. Flag for manual confirmation, do not treat as certain. Real case: Zeria Pharmaceutical Co. Ltd v. Deputy Controller of Patents, Delhi HC, C.A.(COMM.IPD-PAT) 452/2022, judgment 2025-05-27 -- ethoxy-to-methoxy ester swap held an obvious modification, refusal affirmed for lack of proven efficacy.