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Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

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Asymmetric Cation-Olefin Monocyclization by Engineered Squalene-Hopene Cyclases.

Michael Eichenberger¹, Sean Hüppi^1,2, David Patsch^1,3

¹Zurich University of Applied Sciences, Life Sciences and Facility Management, Einsiedlerstrasse 31, 8820, Wädenswil, Switzerland.

Angewandte Chemie (International Ed. in English)

|August 4, 2021

Summary

Researchers engineered squalene-hopene cyclases (SHCs) to produce enantiopure cyclic terpenoids. A novel enzyme variant achieved high yields of (R)-γ-dihydroionone and complementary (S)-enantiomers, overcoming previous selectivity limitations.

Keywords:

chemoenzymatic synthesis cyclization protein engineering squalene-hopene cyclases substrate engineering

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Published on: November 27, 2015

Area of Science:

Biocatalysis
Enzymology
Organic Chemistry

Background:

Squalene-hopene cyclases (SHCs) are key enzymes for synthesizing enantiopure cyclic terpenoids.
A significant limitation in SHC catalysis is their inherent (S)-enantioselectivity, restricting access to diverse stereoisomers.
Developing methods for enantio-complementary synthesis is crucial for accessing valuable terpenoid compounds.

Purpose of the Study:

To engineer SHCs for enantio-complementary synthesis of valuable monocyclic terpenoids.
To identify novel SHC homologs with altered stereoselectivity.
To optimize enzyme and process conditions for enhanced product yield and enantiomeric excess.

Main Methods:

Construction and screening of an 18-member SHC-wild-type library.
Identification and characterization of a novel SHC, AciSHC, exhibiting (R)-enantioselectivity.
Enzyme and process optimization to improve conversion rates and enantioselectivity.
Stereochemical analysis of products derived from different geometric isomers of geranylacetone.

Main Results:

A novel SHC (AciSHC) was discovered, capable of synthesizing (R)-γ-dihydroionone from geranylacetone with optimized conversion up to 79%.
AciSHC variants demonstrated precise differentiation between geranylacetone isomers, yielding (R)-γ-dihydroionone (>99% ee) from the (Z)-isomer and (S,S)-bicyclic ether (>95% ee) from the (E)-isomer.
The stereodivergent catalytic capabilities were extended to achieve the complementary (S)-γ-dihydroionone (>99.9% ee) using an additional SHC-substrate pair.

Conclusions:

Engineered SHCs, particularly AciSHC and its variants, provide a powerful platform for the stereoselective synthesis of enantiopure cyclic terpenoids.
The ability to control enantioselectivity based on substrate isomer offers a novel strategy for accessing both (R)- and (S)-enantiomers of valuable terpenoids.
This work expands the synthetic utility of SHCs, overcoming previous limitations and opening new avenues for industrial applications in terpenoid production.