A stereoselective synthesis of the bromopyrrole natural product (-)-agelastatin A

Stereocontrolled synthesis of vicinal diamines by organocatalytic asymmetric Mannich reaction of N-protected aminoacetaldehydes: formal synthesis of (-)-agelastatin A

The 1,2-diamine (vicinal diamine) motif is present in a number of natural products with interesting biological activity and in many chiral molecular catalysts. The efficient and stereocontrolled synthesis of enantioenriched vicinal diamines is still a challenge to modern chemical methodology. We report here both syn- and anti-selective asymmetric direct Mannich reactions of N-protected aminoacetaldehydes with N-Boc-protected imines catalyzed by proline and the axially chiral amino sulfonamide (S)-3. This organocatalytic process represents the first example of a Mannich reaction using Z- or Boc-protected aminoacetaldehyde as a new entry of α-nitrogen functionalized aldehyde nucleophile in enamine catalysis. The obtained optically active vicinal diamines are useful chiral synthons as exemplified by the formal synthesis of (-)-agelastatin A.

Total syntheses of (-)-hanishin, (-)-longamide B, and (-)-longamide B methyl ester via a novel preparation of N-substituted pyrrole-2-carboxylates [corrected]

A novel preparation of N-substituted pyrrole-2-carboxylates has been developed based upon 1,3-dipolar cycloaddition and a conventional hydrogenolysis. By using this method as the key step, total syntheses of natural alkaloids (-)-hanishin, (-)-longamide [corrected] B, and (-)-longamide [corrected] B methyl ester were accomplished in the highest overall yields, respectively.

Transition-metal-catalyzed aminations and aziridinations of C-H and C=C bonds with iminoiodinanes

Catalytic insertion or addition of a metal-imido/nitrene species, generated from reaction of a transition-metal catalyst with iminoiodanes, to C-H and C=C bonds offers a convenient and atom economical method for the synthesis of nitrogen-containing compounds. Following this groundbreaking discovery during the second half of the last century, the field has received an immense amount of attention with a myriad of impressive metal-mediated methods for the synthesis of amines and aziridines having been developed. This review will cover the significant progress made in improving the efficiency, versatility and stereocontrol of this important reaction. This will include the various iminoiodanes, their in situ formation, and metal catalysts that could be employed and new ligands, both chiral and non-chiral, which have been designed, as well as the application of this functional group transformation to natural product synthesis and the preparation of bioactive compounds of current therapeutic interest.

Copper-catalyzed iminoiodane-mediated aminolactonization of olefins: application to the synthesis of 5,5-disubstituted butyrolactones

A copper(I)-catalyzed reaction of a variety of 4-aryl-pent-4-enoates with nosyliminoiodane generated in situ provides the corresponding 5-aryl-5-nosylamidomethylbutyrolactones. The reaction presumably proceeds via an aziridine intermediate, which could be isolated in one case.

Aziridines from intramolecular alkene aziridination of sulfamates: reactivity toward carbon nucleophiles. application to the synthesis of spisulosine and its fluoro analogue

Catalytic intramolecular alkene aziridination of sulfamate is an emerging methodology for the asymmetric synthesis of chiral functionalized amines involving the formation of bicyclic aziridines. This study demonstrates the ability of the latter to undergo ring-opening with various carbon nucleophiles: Grignard reagents, lithium salts of terminal alkynes, dithiane, malonate. These S(N)2-type reactions occur with high levels of regio- and chemoselectivity to generally afford seven-membered cyclic sulfamidates in good yields. Carbon nucleophiles have also been found to react with these sulfamidates provided that the sulfamate ester has been previously activated by introduction of a tosyl substituent on the NH group. The versatility of this strategy has been illustrated with the syntheses of spisulosine and its fluoro analogue.

Biosynthesis, asymmetric synthesis, and pharmacology, including cellular targets, of the pyrrole-2-aminoimidazole marine alkaloids

The pyrrole-2-aminoimidazole (P-2-AI) alkaloids are a growing family of marine alkaloids, now numbering well over 150 members, with high topographical and biological information content. Their intriguing structural complexity, rich and compact stereochemical content, high N to C ratio (~1 : 2), and increasingly studied biological activities are attracting a growing number of researchers from numerous disciplines world-wide. This review surveys advances in this area with a focus on the structural diversity, biosynthetic hypotheses with increasing, but still rare, verifying experimental studies, asymmetric syntheses, and biological studies, including cellular target receptor isolation studies, of this stimulating and exciting alkaloid family.

Chiral molecules containing the pyrrole framework

Synthetic routes to chiral molecules containing a pyrrolic ring are discussed: strategies include formation of the pyrrole ring using starting materials appended with chirality, as well as the attachment of chirality to a pre-formed pyrrole.

Total synthesis of all (-)-Agelastatin alkaloids

The pyrrole-imidazole family of marine alkaloids, derived from linear clathrodin-like precursors, constitutes a diverse array of structurally complex natural products. The bioactive agelastatins are members of this family that possess a tetracyclic molecular framework incorporating C4-C8 and C7-N12 bond connectivities. We provide a hypothesis for the formation of the unique agelastatin architecture that maximally exploits the intrinsic chemistry of plausible biosynthetic precursors. We report the concise enantioselective total syntheses of all known agelastatin alkaloids including the first total syntheses of agelastatins C, D, E, and F. Our gram-scale chemical synthesis of agelastatin A was inspired by our hypothesis for the biogenesis of the cyclopentane C-ring and required the development of new transformations including an imidazolone-forming annulation reaction and a carbohydroxylative trapping of imidazolones.

Total synthesis of the beta-catenin inhibitor, (-)-agelastatin A: a second-generation approach based on radical aminobromination

The second-generation approach to (-)-agelastatin A has been established. The present strategy features the FeBr(2)-mediated radical cyclization of 2-cyclopentenyloxycarbonyl azide that allows for the stereoselective installation of a cis-vicinal aminobromo functionality suitable for producing the BCD-ring system of agelastatin A. The aminobromination method streamlines access to oxazolidinone, a key intermediate in the previously reported synthesis, thereby culminating in the new total synthesis of (-)-agelastatin A.

A submarine journey: the pyrrole-imidazole alkaloids

In his most celebrated tale "The Picture of Dorian Gray", Oscar Wilde stated that "those who go beneath the surface do so at their peril". This sentence could be a prophetical warning for the practitioner who voluntarily challenges himself with trying to synthesize marine sponge-deriving pyrrole-imidazole alkaloids. This now nearly triple-digit membered community has been growing exponentially in the last 20 years, both in terms of new representatives and topological complexity--from simple, achiral oroidin to the breathtaking 12-ring stylissadines A and B, each possessing 16 stereocenters. While the biosynthesis and the role in the sponge economy of most of these alkaloids still lies in the realm of speculations, significant biological activities for some of them have clearly emerged. This review will account for the progress in achieving the total synthesis of the more biologically enticing members of this class of natural products.

Total synthesis of (-)-agelastatin A: the application of a sequential sigmatropic rearrangement

An enantioselective total synthesis of (-)-agelastatin A from (-)-2,3-O-isopropylidene-d-threitol is described. The sequential Overman/Mislow-Evans rearrangement of the allylic bistrichloroimidate is the key step, which efficiently installed a diaminohydroxy group.