Abstract
Vitamin E-related tocochromanols include the rare homologs tocomonoenol (TM) and tocodienol (TD), containing one and two side-chain double bonds, respectively. This review critically evaluates their structural diversity, biosynthesis, natural occurrence, biological activities, and biotechnological potential. Recent analytical studies identify 11′-TM homologs, particularly 11′-α-TM and 11′-γ-TM, in plant oils and photosynthetic microorganisms, whereas 12′-α-TM, known as marine-derived tocopherol (MDT), is associated with cold-water marine organisms. Genetic evidence supports a VTE1/VTE2-dependent pathway for TM formation involving partially reduced prenyl precursors. Chemical partial hydrogenation of tocotrienols can generate TM and TD, while targeted microbial production remains a potential but unvalidated strategy. Cellular studies demonstrate the uptake and metabolism of 11′-TM, whereas antioxidant, anti-inflammatory, and adipocyte-related effects have been reported primarily for MDT. Preliminary evidence also suggests antiproliferative effects of α-TM in prostate cancer cell models, although therapeutic relevance remains unestablished. Importantly, the endogenous biosynthetic pathway of TD remains unresolved, and direct cellular and in vivo evidence for the biological activity of naturally occurring TD is lacking. Consequently, its physiological and therapeutic significance cannot yet be established. Future research should prioritize isotope tracing, candidate-enzyme validation, purified-compound pharmacokinetics, and compound-specific toxicological evaluation. Overall, TM shows emerging biological potential, whereas TD remains a major biosynthetic and functional knowledge gap.