Substrate encapsulation: an efficient strategy for the RCM synthesis of unsaturated epsilon-lactones

Ring-Closing Metathesis on Commercial Scale: Synthesis of HCV Protease Inhibitor Simeprevir

The key macrocyclization step in the synthesis of simeprevir, a hepatitis C virus (HCV) antiviral drug, was studied. N-Boc substitution on the diene precursor changes the site of insertion of the metathesis catalyst and, consequently, the kinetic model of the ring closing metathesis (RCM), enabling a further increase in the macrocyclization efficiency under simulated high dilution (SHD) conditions. NMR of the inserted species of both first and second generation RCM catalysts are reported and discussed.

Synthesis and antifungal activity of 7-methyl-7-hydroxy-2,3-benzo[c]octa-1,6-olide

The racemic 7-methyl-7-hydroxy-2,3-benzo[c]octa-1,6-olide, the analog of natural product (6R)-3,7-dimethyl-7-hydroxy-2-octen-1,6-olide, was totally synthesized using easily available (E)-2-(2-carboxyvinyl)benzoic acid as a raw material in nine-step reactions including three key steps of Wittig reaction, epoxidation, and cyclization, with an overall yield of 10.3%. The bioassay results showed that ( ± )-2 exhibited stronger antifungal activity than the natural product ( ± )-1 and (R)-1 against Alternaria solani with an EC₅₀ value of 27.36 μg/ml.

Total synthesis of 3,7-dimethyl-7-hydroxy-2-octen-1,6-olide and 3,7-dimethyl-2,6-octadien-1,6-olide

3,7-Dimethyl-7-hydroxy-2-octen-1,6-olide and 3,7-dimethyl-2,6-octadien-1,6-olide, the natural bioactive compounds isolated from the fruit of Litsea cubeba and the liverwort Plagiochila rutilans, were totally synthesized using easily available cis-geraniol as raw material in short, convenient, and low-cost, five-step reactions including three steps of oxidation, cyclization, and dehydration, with an overall yield of 47.5% and 37.3%.

Ring-chain equilibria of R-but-3-enoate esters — A quantum mechanical study of direct and indirect ring-closing reactions

Macrocyclic structures can be synthesized through two simultaneous olefin metathesis reactions: either directly through ring-closing metathesis (RCM) or indirectly through an intermediate formed by acyclic diene metathesis (ADMET). The proclivity of a homologous series of 16 R-but-3-enoate esters to form lactones through one of these two processes is studied at the HF/6–31G(d), B3LYP/6–31G(d), and MP2(full)/6–31G(d) levels of theory. Computed Gibbs free energies are used to determine ΔGRCM, ΔGADMET, and ΔΔG (ΔGRCM – ΔGADMET). ΔΔG is evaluated to compare the relative favourability of the RCM and ADMET reactions for the various R-but-3-enoate esters, where each system is differentiated by the number of methylene groups (n) added to the ester chain. When n = 0, 1, 10, or 13, cyclic lactone formation by direct RCM is predicted to be thermodynamically favoured, and the indirect synthesis is preferred for all other heterocyclic structures. The same trend holds between 298.15 and 333.15 K, therefore, the gas-phase model is a reasonable approximation of the experimental reaction conditions. The theoretical model is sufficient for smaller systems, but molecules larger than the n = 6 case do not follow experimental results for similar saturated structures. Hence, the assumptions pertaining to straight-chain and cis-ring conformations need to be re-evaluated. In particular, chain flexibility should be further examined.