Stability Study of Alpinia galanga Constituents and Investigation of Their Membrane Permeability by ChemGPS-NP and the Parallel Artificial Membrane Permeability Assay

Alpinia galanga Willd., greater galangal, has been used for thousands of years as a spice as well as in traditional medicine. Its central nervous system (CNS) stimulant activity and neuroprotective effects have been proved both in animal models and human trials. However, the compounds responsible for these effects have not been identified yet. Therefore, the main constituents (p-OH-benzaldehyde (1), trans-p-coumaryl-alcohol (2), p-coumaryl-aldehyde (4), galanganol A (5), galanganol B (6), trans-p-acetoxycinnamyl alcohol (7), 1′S-1′-acetoxychavicol acetate (ACA, 9), and 1′S-1′-acetoxyeugenol acetate (AEA, 10)) were isolated to investigate their aqueous stability and passive diffusion across the gastro-intestinal tract (GIT) membrane and the blood–brain barrier (BBB) by the parallel artificial membrane permeability assay (PAMPA). Our positive results for compounds 1, 2, 4, 7, 9, and 10 suggest good permeability, thus potential contribution to the effects of greater galangal in the CNS. The results of the PAMPA-BBB were corroborated by in silico chemography-based ChemGPS-NP framework experiments. In addition, examination of the chemical space position of galangal compounds in relation to known psychostimulants revealed that all the molecules in proximity are NET/SERT inhibitors. As ACA and AEA did not show much proximity to either compound, the importance of further investigation of their degradation products becomes more pronounced.