Ruzicha Echenmoser Arigoni

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Ruzicha Echenmoser Arigoni Triterpene
Cyclization Rules (mid-1950s) 1 Cyclization
occurs from all-trans squalene epoxide. 2 - The
squalene chain is specifically oriented (folded)
by the cyclizing enzyme into a series of
potential chair and boat cyclohexane rings. 3 -
Cyclization occurs via a sequence of trans
additions to the double bonds all
operations (i.e. cyclizations, Wagner-Meerwein
rearrangements and 1,2 eliminations) are only
allowed under optimal stereoelectronic
conditions, e.g. anti-periplanar parallel
arrangement of double bonds. 4 - All
cyclizations and transformations of squalene
epoxide to product occur non-stop no
stabilized, independent intermediate is
formed.