Nuclear magnetic resonance (NMR) analysis of the obtained compounds revealed that they did not have the expected six-membered ring structure with 1,5 cyclization, but all compounds had fivemembered ring structures with 1,4 cyclization (D-glucono-1,4-lactone: 1,4-GL). This was confirmed using heteronuclear multiple bond correlation (HMBC)-NMR. Specifically, a cross-peak from the hydrogen at position 4 to the carbon at position 1 and a cross-peak from the hydrogen at position 5 to the carbonyl carbon of the fatty acid were observed for each compound. The reaction was conducted at room temperature for one day, followed by 4 h at 80°C. b Isolated yield purified using column chromatography. c Isolated yield purified using crystallization.