Lactam Ent-kaurane Diterpene: A new class of diterpenoids present in roasted beans of Coffea arabica.

Seven new lactam ent-kaurane diterpenoids, cafemides A-G (1-7), were isolated from roasted beans of Coffea arabica. Their structures were elucidated by extensive spectroscopic analysis including 1D, 2D NMR (heteronuclear single quantum correlation (HSQC), heteronuclear multiple bond correlation (HMBC), H-1-H-1 correlation spectroscopy (COSY), and rotating frame Overhauser effect spectroscopy (ROESY)), high-resolution electrospray ionization mass spectrometry (HRESIMS), and IR spectra. They were divided into subtype I-III according to the structure. Further, with the aid of liquid chromatography-tandem mass spectrometry (LC-MS/MS) based molecular network, seven (8-14) subtype II diterpenoids were successfully identified. In addition, a variety of other subtypes of N-containing diterpenoids have been proven in roasted coffee. Compounds 1, 2, 3, 5, and 7 showed a moderate inhibitory effect on alpha-glucosidase with an IC50 value of 8.28 +/- 0.62 mu M, 38.23 +/- 8.87 mu M, 28.94 +/- 1.42 mu M, 12.44 +/- 1.37 mu M, and 22.2 +/- 5.34 mu M, respectively. To the best of our knowledge, this is the first time that N-containing diterpenoids have been reported in coffee.