[Structural analyses of barbaloin-related compounds in aloe drinks]

Four kinds of barbaloin (BA)-related compounds (A, B, C, D) in aloe drinks were isolated by using preparative HPLC. LC/MS analyses of these compounds showed the identical quasimolecular ion peak at m/z 833 [M-H]-. The chemical structures were mainly determined by NMR, including 1H-1H two-dimensional correlation spectroscopy (COSY), nuclear Overhauser and exchange spectroscopy (NOESY), heteronuclear multiple quantum coherence (HMQC), and heteronuclear multiple-bond connectivity (HMBC) experiments. They were identified as BA-related compounds A (10R, 10"S), B (10S, 10"S), C (10S, 10"R), and D (10R, 10"R) coupled through a C-10 to C-7' linkage, and newly found in nature. These results suggested that BA is converted to dimers during storage of aloe drinks.