Total Synthesis Of Lamellarin Research Articles

Total Synthesis of Lamellarins U and A3 by Interrupting Halogen Dance

AbstractA total synthesis of lamellarins U and A3 is described. The synthesis features the interruption of a halogen dance reaction of a metalated α,β-dibromopyrrole. The pyrrolylmagnesium reagent, generated by deprotonative metalation by using (TMP)MgCl·LiCl (TMP = 2,2,6,6-tetramethylpiperidide) as the base, was transmetalated to the corresponding organozinc species without causing the halogen dance reaction, which underwent a Negishi coupling to incorporate an aryl group onto the pyrrole ring. The arylated α,β-dibromopyrrole was then converted into lamellarins U and A3 through an α-selective halogen–magnesium exchange followed by carboxylation and subsequent palladium-mediated cyclization. The late-stage introduction of another aryl group was performed using a Kosugi–Migita–Stille coupling to provide lamellarins U and A3.

Modular Total Syntheses of Lamellarin G Trimethyl Ether and Lamellarin S

AbstractModular total syntheses of the title compounds 2 and 3 are reported. The key pyrrolic building block 8 was prepared from the readily accessible pyrrole 6 via a di‐iodination/mono‐deiodination sequence. Suzuki–Miyaura cross‐coupling of compound 8 with boronate ester 9 afforded lactone 10. Bromination of compound 10 followed by N‐alkylation under Mitsunobu conditions afforded the fully substituted pyrrole 13 that engaged in a second Suzuki–Miyaura cross‐coupling reaction with boronic acid 14 to give compound 15. Hydrolysis of the ester moiety within the last compound afforded acid 16 that engaged in a decarboxylative Heck cyclization process to give lamellarin G trimethyl ether (3). A related sequence of reactions starting from building block 8 and using the isopropoxy‐substituted arenes 22, 25 and 27 has allowed for the completion of the first total synthesis of lamellarin S (2).

Total Synthesis of Lamellarins D (Ia), L (II), and N (Ib).

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The first total synthesis of lamellarin α 20-sulfate, a selective inhibitor of HIV-1 integrase

The first total synthesis of lamellarin α 20-sulfate ( 1), a selective inhibitor of HIV-1 integrase, has been completed. The lamellarin α core in which 13-OH and 20-OH were differentially protected by isopropyl and benzyl groups, respectively, was constructed by using Hinsberg-type pyrrole synthesis and Suzuki–Miyaura coupling as the key reactions. The 20-sulfate was prepared by a sequence including debenzylation of 20-OBn, 2,2,2-trichloroethylsulfation of the resulting 20-OH, deprotection of 13-O i-Pr, and final reductive cleavage of the 2,2,2-trichloroethyl ester.

Total synthesis of lamellarins D, L, and N

Total synthesis of cytotoxic marine alkaloids, lamellarins D, L, and N, has been achieved by using Hinsberg-type pyrrole synthesis and palladium-catalyzed Suzuki–Miyaura coupling of the 3,4-dihydroxypyrrole bistriflate 6 as the key reactions. The total yields of lamellarins D, L, and N from the common intermediate 6 are 54, 58, and 50%, respectively.

Utility of Polymer-Supported Reagents in the Total Synthesis of Lamellarins

Four solid-supported reagents have been utilized in the multistep synthesis of lamellarins. The use of Amberlyst A-26 Br(3)(-) and polymer bound pyridine hydrobromide perbromide (PVPHP) for keto alpha-bromination of the less studied ortho-substituted acetophenone derivatives selectively furnished the corresponding monobromination products (phenacyl bromide derivatives), which were used directly in condensation reactions with benzyldihydroisoquinoline mediated by Amberlyst A-26 NaCO(3)(-). The 2H-pyrrole carbonates subsequently underwent intramolecular Friedel-Crafts transacylation followed by lactonization to provide the lamellarin skeleton. Alternatively, Amberlyst A-26 NaCO(3)(-) effectively served as base in condensation reaction of benzyldihydroisoquinoline with alpha-nitrocinnamate derivatives to provide the corresponding 2-ethoxycarbonyl pyrroles, which smoothly underwent O-debenzylation reaction followed by lactonization to furnish the lamellarin skeleton. The novel Amberlyst-15 mediated lactonization reactions effectively combined the otherwise two separate steps into a single transformation.

A Modular Synthesis of the Lamellarins: Total Synthesis of Lamellarin G Trimethyl Ether.

A modular synthesis of the lamellarin family of natural products has been developed that is based on the application of three iterative halogenation/cross-coupling reaction sequences. The ability to halogenate the pyrrole core in a regioselective fashion, even in the presence of highly electron-rich aryl substituents, has been established. The compatibility of Suzuki coupling conditions with free alcohols and phenols in the boronic acids has been employed to reduce the number of protection/deprotection steps. Indeed, the presence of a free phenol on boronic acid 3 has been determined to be critical for the successful final coupling in route to lamellarin G trimethyl ether, since protected versions fail to undergo coupling.

Short and flexible route to 3,4-diarylpyrrole marine alkaloids: syntheses of permethyl storniamide A, ningalin B, and lamellarin G trimethyl ether

A highly efficient route to 3,4-diarylpyrrole marine alkaloids has been developed using Hinsberg-type pyrrole synthesis and palladium-catalyzed Suzuki cross-coupling of the 3,4-dihydroxypyrrole bis-triflate derivatives as key reactions. Based on this approach, formal syntheses of permethyl storniamide A and ningalin B, and a total synthesis of lamellarin G trimethyl ether have been achieved.