Organocatalytic Michael Addition of Aldehydes to Protected 2-Amino-1-Nitroethenes: The Practical Syntheses of Oseltamivir (Tamiflu) and Substituted 3-Aminopyrrolidines

Asymmetric organocatalysis at the service of medicinal chemistry

The application of the most representative and up-to-date examples of homogeneous asymmetric organocatalysis to the synthesis of molecules of interest in medicinal chemistry is reported. The use of different types of organocatalysts operative via noncovalent and covalent interactions is critically reviewed and the possibility of running some of these reactions on large or industrial scale is described. A comparison between the organo- and metal-catalysed methodologies is offered in several cases, thus highlighting the merits and drawbacks of these two complementary approaches to the obtainment of very popular on market drugs or of related key scaffolds.

Enantioselective Michael additions of aldehydes to nitroalkenes catalyzed with ionically tagged organocatalyst

Enantioselective organocatalytic Michael additions affords useful building blocks for many biologically and medicinally relevant compounds. Ionically-tagged diphenylprolinol silyl ether efficiently catalyzes several Michael additions of aldehydes to nitroalkenes in ionic liquids. The Michael additions work well in ionic liquids; yields up to 95% and enantioselectivities up to 95% ee were achieved. Furthermore, in some cases, the catalytic system was reusable.

Stereoselective construction of all-carbon quaternary center by means of chiral phosphoric acid: highly enantioselective Friedel–Crafts reaction of indoles with β,β-disubstituted nitroalkenes

Chiral phosphoric acid catalyzed Friedel–Crafts reaction of indoles with β-alkoxycarbonyl-β-disubstituted nitroalkenes was achieved.

Unusual anti-selective asymmetric conjugate addition of aldehydes to nitroalkenes catalyzed by a biphenyl-based chiral secondary amine

Unusual anti-selectivity was observed in the conjugate addition of aldehydes to nitroalkenes, when a biphenyl-based chiral secondary amine was used as catalyst.

Synthesis of the tetracyclic core of Illicium sesquiterpenes using an organocatalyzed asymmetric Robinson annulation

An enantioselective synthesis of the core framework of neurotrophic Illicium majucin-type sesquiterpenes is described here. This strategy is based on an organocatalyzed asymmetric Robinson annulation and provides an efficient approach for a diversity-oriented synthesis of Illicium natural products that holds remarkable therapeutic potential for neurodegenerative diseases.

Two approaches toward the formal total synthesis of oseltamivir phosphate (Tamiflu): catalytic enantioselective three-component reaction strategy and L-glutamic acid strategy

Two independent formal total syntheses of oseltamivir phosphate were successfully achieved: the first utilized a copper-catalyzed asymmetric three-component reaction strategy, and the second utilized L-glutamic acid γ-ester as a chiral source to install the correct stereochemistry. Both strategies used Dieckmann condensation to construct a six-membered ring core, after which manipulation of the functional groups and protecting groups accessed Corey's intermediate for the synthesis of oseltamivir phosphate. While the first synthesis was accomplished via four purification steps in 25.7% overall yield, albeit with moderate optical purity (76% ee), the second strategy achieved the synthesis via six purification steps in 19.8% overall yield with perfect enantiocontrol.

Synthesis of (-)-oseltamivir phosphate (Tamiflu) starting from cis-2,3-bis(hydroxymethyl)aziridine

Oseltamivir phosphate (Tamiflu) has been synthesized from cis-2,3-bis(hydroxymethyl)aziridine. After protection of the cis-2,3-bis(hydroxymethyl)aziridine with a Boc group, desymmetrization provided a chiral aziridine, which was a key intermediate to install the required stereogenic center containing a nitrogen atom. Allylation and ring closing metathesis are the key reactions to obtain the cyclic product that was successfully converted to the desired oseltamivir phosphate.

Synthesis of highly functionalized β-aminocyclopentanecarboxylate stereoisomers by reductive ring opening reaction of isoxazolines

A rapid and simple procedure was devised for the synthesis of multifunctionalized cyclic β-amino esters and γ-amino alcohols via the 1,3-dipolar cycloaddition of nitrile oxides to β-aminocyclopentenecarboxylates. The opening of the isoxazoline reductive ring to the corresponding highly functionalized 2-aminocyclopentanecarboxylates occurred stereoselectively with good yields.

Several generations of chemoenzymatic synthesis of oseltamivir (Tamiflu): evolution of strategy, quest for a process-quality synthesis, and evaluation of efficiency metrics

Four generations of chemoenzymatic approaches to oseltamivir are presented. The first two generations relied on the use of cyclohexadiene-cis-diol derived enzymatically from bromobenzene. The third and fourth generation used the corresponding diol obtained from ethyl benzoate by fermentation with E. coli JM109(pDTG601a). Oseltamivir was obtained from ethyl benzoate by intersecting intermediate 39 (third-generation synthesis) and intermediate 45 (fourth-generation synthesis). Both of these advanced approaches benefited from symmetry considerations and translocation of the acrylate double bond with concomitant elimination of the C-1 hydroxyl. The syntheses are evaluated for overall efficiency by the use of efficiency metrics and compared with other syntheses of oseltamivir (both academic and industrial).