Enantioselective Total Synthesis of (+)-Amphirionin-4

Design of substituted tetrahydrofuran derivatives for HIV-1 protease inhibitors: synthesis, biological evaluation, and X-ray structural studies

Substituted tetrahydrofuran derivatives were designed and synthesized to serve as the P2 ligand for a series of potent HIV-1 protease inhibitors. Both enantiomers of the tetrahydrofuran derivatives were synthesized stereoselectivity in optically active forms using lipase-PS catalyzed enzymatic resolution as the key step. These tetrahydrofuran derivatives are designed to promote hydrogen bonding and van der Waals interactions with the backbone atoms in the S2 subsite of the HIV-1 protease active site. Several inhibitors displayed very potent HIV-1 protease inhibitory activity. A high-resolution X-ray crystal structure of an inhibitor-bound HIV-1 protease provided important insight into the ligand binding site interactions in the active site.

Palladium-Catalyzed Double Reductive Cyclization of 2,3-Dinitro-1,4-dialkenylbenzenes. Synthesis of 1H,8H-Pyrrolo[3,2-g]indoles

A flexible route to both symmetrical and unsymmetrical 1H,8H-pyrrolo[3,2-g]indole has been developed. The key and ultimate step is a double palladium-catalyzed, carbon monoxide mediated reductive cyclization of 1,4-dialkenyl-2,3-dinitrobenzenes. The cyclization precursors were prepared by a double Kosugi-Migita-Stille cross coupling of 1,4-dibromo-2,3-dinitrobenzene with an alkenyltin reagent to give symmetrical products. Unsymetrical cyclization precursors were prepared by two sequential cross couplings using 4-iodo-2,3-dinitrophenyl trifluoromethanesulfonate as the starting material.

Enantioselective Total Synthesis of (+)-Monocerin, a Dihydroisocoumarin Derivative with Potent Antimalarial Properties

We describe here the enantioselective synthesis of (+)-monocerin and its acetate derivative. The present synthesis features an efficient optically active synthesis of the β-hydroxy-γ-lactone derivative with high enantiomeric purity using Sharpless dihydroxylation as the key step. The synthesis also highlights a tandem Lewis acid-catalyzed, oxocarbenium ion-mediated diastereoselective syn-allylation reaction, and a methoxymethyl group promoted methylenation reaction. We investigated this reaction with a variety of Lewis acids. A selective CrO3-mediated oxidation of isochroman provided the corresponding lactone derivative. The synthesis is quite efficient and may be useful for the preparation of derivatives.

Bifunctional Ligand Enables Efficient Gold-Catalyzed Hydroalkenylation of Propargylic Alcohol

Using the previously designed biphenyl-2-ylphosphine ligand, featuring a remote tertiary amino group, the first gold-catalyzed intermolecular hydroalkenylation of alkynes has been developed. Synthetically valuable conjugated dienyl alcohols are formed in moderate to good yields. A range of alkenyltrifluoroborates are allowed as the alkenyl donor, and no erosion of alkene geometry and/or the propargylic configuration are detected. DFT calculations confirm the critical role of the remote basic group in the ligand as a general-base catalyst for promoting this novel gold catalysis with good efficiency.

Concise Total Synthesis of (±)-Deguelin and (±)-Tephrosin Using a Vinyl Iodide as a Key Building Block

A concise and protecting-group-free total synthesis of the antiproliferative natural product (±)-deguelin (2) was accomplished in four steps and 62% overall yield from commercially available precursors. The key transformation employed a vinyl iodide as the pivotal building block to construct the 4-acylchromene substructure present in deguelin. Subsequent Cu₂O-mediated α-hydroxylation of deguelin (2) afforded tephrosin (3) in 90% yield.

Synthesis and Photooxidation of the Trisubstituted Oxazole Fragment of the Marine Natural Product Salarin C

The eastern section of the macrocyclic marine natural product salarin C from the sponge Fascaplysinopsis sp. was synthesized employing a halogen dance reaction to assemble the trisubstituted oxazole moiety. The synthesis was inspired by Kashman's hypothesis on the biomimetic oxidation of salarin C to salarin A. Clean conversion to the triacylamine partial structure of salarin A occurred on treatment with photochemically generated singlet oxygen. Thus, a Wasserman-type oxidative rearrangement is chemically possible in this case.

Total syntheses of both enantiomers of amphirionin 4: A chemoenzymatic based strategy for functionalized tetrahydrofurans

The total syntheses of (-)-amphirionin-4 and (+)-amphirionin-4 have been achieved in a convergent and enantioselective manner. The tetrahydrofuranol cores of amphirionin-4 were constructed in optically active form by enzymatic resolution of racemic cis-3-hydroxy-5-methyldihydrofuran-2(3H)-one. The polyene side chain was efficiently synthesized using Stille coupling. The remote C8-stereocenter was constructed using the Nozaki-Hiyama-Kishi coupling reaction. A detailed ¹H-NMR studies of Mosher esters of (-)-amphirionin-4 and (+)-amphirionin-4 were carried out to support the assignment of the absolute configurations of C-4 and C-8 asymmetric centers of amphirionin-4.