Abstract
ABSTRACT Advances in Nuclear Magnetic Resonance (NMR) spectroscopy is a cornerstone in structure elucidation of polycyclic 'cage' scaffolds. Due to the compactness of these compounds, much overlap, as well as unique through-space and bond NMR interactions are frequently observed. This review serves as a guide for the NMR elucidation of future derivatives by providing some of the typical and relevant aspects of the characteristic trends, substituent patterns and chemical shift behaviour for the identification of the polycyclic structures, namely adamantane, pentacycloundecane and trishomocubane derivatives. Keywords: adamantane, NMR elucidation, pentacycloundecane, polycyclic compounds, trishomocubane
Highlights
The chemistry of polycyclic ‘cage’ scaffolds has fascinated organic chemists for over six decades.[1-8]
The data provided by 1D Nuclear Magnetic Resonance (NMR) spectroscopy is much simpler to analyse; it typically does not provide enough information to fully elucidate these compounds. 2D NMR spectroscopy allows for structure elucidation by determining the proximity and effects of protons on carbons or other protons via bond/space interactions. 2D NMR spectroscopy is especially useful for structural elucidation of similar compounds, as there are typical patterns that can
After analysing a variety of literature, it can be concluded that adamantane, pentacycloundecane, and trishomocubane have unique NMR patterns
Summary
The chemistry of polycyclic ‘cage’ scaffolds has fascinated organic chemists for over six decades.[1-8] These compounds include adamantane, pentacycloundecane, trishomocubane, pentacyclodecane, cubane, basketane (Figure 1). The effect of the unusual cage geometries on chemical reactivity,[9] and more importantly, its role in pharmacological profiles have been and still are investigated Application of these compounds in drug discovery stems from the polycyclic cage compounds ability to increase drug lipophilicity[10], serving as a transport aid to carry such drug pharmacophores across cellular membranes, including the blood-brain barrier (BBB) and the central nervous system (CNS).[8, 11-16]. This review summarises the 1H and 13C NMR data of 20 adamantane, 69 pentacycloundecane and 8 trishomocubane derivatives in the bid to establish tendencies; this will be a useful tool for future structural elucidation of these classes of polycyclic compounds. We provide an account on the progress in the NMR elucidation using two-dimensional NMR techniques for the most commonly reported polycyclic cage families, namely: adamantane, pentacycloundecane and trishomocubane
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