Exploring the Chemical Space around Cannabis sativa L. Leaves as a Source of Bioactive Compounds of Pharmaceutical Interest

Cannabis sativa L. is a plant with a complex chemical profile of secondary metabolites, well established especially for what concerns inflorescences. Other parts of the plant, such as the leaves, are usually considered a waste material from the hemp industry and, therefore, are not yet considered in the research field. In this study, the leaves of four non-psychotropic C. sativa (hemp) varieties, including a CBD-, a CBG-, a CBC-type, and a cannabinoid-free one, were comprehensively characterized for their qualitative and quantitative composition of polyphenols, cannabinoids, policosanols, and terpenes. In addition, the present work also aimed at the development of an extraction and analytical method for quantification of squalene from the leaves of the four hemp chemotypes, in the perspective of finding an alternative plant source to recover this compound. Analytical techniques applied included UHPLC-HRMS and GC-MS for compound identification, while HPLC-UV/Vis, HPLC-ELSD, and GC-FID for quantification purposes. Cannflavin A and B were the predominant non-cannabinoid phenolic compound in the leaves. Among cannabinoids, cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), and cannabichromenic acid (CBCA) were the most abundant compounds in the analyzed samples. Minor CBD-type and CBG-type cannabinoids were detected in the leaves. The analysis of policosanols was focused on C ₂₄ OH, C ₂₆ OH, C ₂₈ OH, C ₃₀ OH, and C ₃₂ OH as the main compounds. Squalene was isolated, fully characterized for the first time from hemp leaves, and it was identified and quantified by using GC-MS and GC-FID techniques. Terpenes were analyzed by GC-MS; in addition to those commonly found in C. sativa (i.e., β-caryophyllene, α-humulene, α-bisabolol and caryophyllene oxide), some volatile constituents specific for the varieties were also detected.Overall, hemp leaves represent a rich source of bioactive compounds that could be exploited in the pharmaceutical field from a circular economy perspective. This study, in addition, gives new insights into the possibility of hemp as a potential plant-based alternative source of squalene.