Squalene-hopene cyclases (SHCs) have great potential for the industrial synthesis of enantiopure cyclic terpenoids.Alimitation of SHC catalysis has been the enzymes strict (S)-enantioselectivity at the stereocenter formed after the first cyclization step.T ogain enantio-complementary access to valuable monocyclic terpenoids,a nS HC-wild-type library including 18 novel homologs was set up.Apreviously not described SHC (AciSHC) was found to synthesizes mall amounts of monocyclic (R)-g-dihydroionone from (E/Z)geranylacetone.U sing enzyme and process optimization, the conversion to the desired product was increased to 79 %. Notably,a nalyzed AciSHC variants could finely differentiate between the geometric geranylacetone isomers:While the (Z)isomer yielded the desired monocyclic (R)-g-dihydroionone (> 99 %ee), the (E)-isomer was converted to the (S,S)-bicyclic ether (> 95 %e e). Applying the knowledge gained from the observed stereodivergent and enantioselective transformations to an additional SHC-substrate pair,a ccess to the complementary (S)-g-dihydroionone (> 99.9 %ee) could be obtained.

Squalene–hopene cyclases (SHCs) have great potential for the industrial synthesis of enantiopure cyclic terpenoids. A limitation of SHC catalysis has been the enzymes’ strict (S)‐enantioselectivity at the stereocenter formed after the first cyclization step. To gain enantio‐complementary access to valuable monocyclic terpenoids, an SHC‐wild‐type library including 18 novel homologs was set up. A previously not described SHC (AciSHC) was found to synthesize small amounts of monocyclic (R)‐γ‐dihydroionone from (E/Z)‐geranylacetone. Using enzyme and process optimization, the conversion to the desired product was increased to 79 %. Notably, analyzed AciSHC variants could finely differentiate between the geometric geranylacetone isomers: While the (Z)‐isomer yielded the desired monocyclic (R)‐γ‐dihydroionone (>99 % ee), the (E)‐isomer was converted to the (S,S)‐bicyclic ether (>95 % ee). Applying the knowledge gained from the observed stereodivergent and enantioselective transformations to an additional SHC‐substrate pair, access to the complementary (S)‐γ‐dihydroionone (>99.9 % ee) could be obtained.

Dedicated to Prof. Antonio Togni on the occasion of his 65th birthday A low-valent cobalt(I) complex, formed from the reduction of CoBr 2 (dppe) with zinc, acts as catalyst for the efficient [2 + 4] cycloaddition of β-alkyl, cycloalkyl and aryl substituted propiolates to dienes. This transformation yields synthetically relevant 1,4-cyclohexadiene carboxylates in good to excellent yields. Furthermore, the target compounds are novel lead structures for the discovery of fragrance ingredients from the fruity, floral and spicy odor family.

No abstract

No abstract