Synthetic strategies directed to the antitumour alkaloids sesbanimide A and manzamine A

Synthons derived from nature's chiral pool have been utilized in developing strategies aimed at the syntheses of the alkaloids sesbanimide A and manzamine A. The route designed for sesbanimide A has provided the naturally occurring alkaloid and a facile access to several analogues for structure-activity relationship studies. The approach to the synthesis of manzamine A has led to a strategically functionalized chiral tricyclic intermediate possessing the absolute stereochemistry of the natural product. Recent results on the synthesis of sesbanimide analogues and the progress towards the total synthesis of manzamine A is described.     

An access to the bicyclic nucleus of the sponge alkaloid halicyclamine A by successive condensation of malondialdehyde units, aldehyde derivatives, and primary amines

First results of an evaluation of the synthetic sequence depicted in Scheme 4 are reported. This sequence is based upon biosynthetic considerations concerning the manzamine family of sponge alkaloids. Stable equivalents 21 and 31 of the tetraaldehyde 7 have thus been obtained by using the chemistry of malondialdehyde previously reported by Tietze. These compounds afforded pyridinium salts 23 and 33 when treated with a primary amine in acidic medium. Further reductive amination and cyclization yielded bicyclic derivatives 25 and 35, thus demonstrating the feasibility of this synthetic approach for the preparation of halicyclamine derivatives 13. Products resulting from cycloaddition reactions leading to 9 were not observed.     

Neuritogenic activity-guided isolation of a free base form manzamine A from a marine sponge, Acanthostrongylophora aff. ingens (Thiele, 1899)

Two manzamine-class alkaloids, manzamine A (1) and 8-hydroxymanzamine (2) were isolated from a Japanese marine sponge Acanthostrongylophora aff. ingens, together with three known alkaloids manzamine E (3), manzamine F (4), and manzamine X (5). The spectral features of 1 and 2 were different from the reported data. Detailed structure analysis using 2D NMR revealed the structure of 1 and 2 as a free base form of hydrochloric salt. These manzamine-class alkaloids showed neuritogenic activity against Neuro 2a cells.     

Synthesis and biological evaluation of manzamine analogues

[Structure: see text] The synthesis and biological evaluation of a series of analogues of manzamine A, representing partial structures of the pentacyclic ABCDE diamine core, is described. All new compounds were screened against Plasmodium falciparum and demonstrated attenuated antimalarial activity relative to that of manzamine A.     

Enantioselective total syntheses of manzamine a and related alkaloids

As a prelude to undertaking the total syntheses of the complex manzamine alkaloids, a series of model studies were conducted to establish the scope and limitations of intramolecular [4 + 2] cycloadditions of N-acylated vinylogous ureas with the trienic substrates 17a,b, 28a,b, and 34. These experiments clearly demonstrated that the geometry of the internal double bond and the presence of an electron-withdrawing group on the diene moiety were essential for the facile and stereoselective formation of the desired cycloadducts. The enantioselective syntheses of the manzamine alkaloids ircinol A (75), ircinal A (5), and manzamine A (1) were then completed by employing a convergent strategy that featured a novel domino Stille/Diels-Alder reaction to construct the tricyclic ABC ring core embodied in these alkaloids. Thus, the readily accessible chiral dihydropyrrole 58 was first converted in a single chemical operation into the key tricyclic intermediate 60. Two ring-closing metathesis reactions were then used to form the 13- and 8-membered rings leading to Z-72 and 74, the latter of which was quickly elaborated into ircinal A (5) via ircinol A (75). The synthetic 5 thus obtained was converted into manzamine A (1) following literature precedent. This concise synthesis of ircinal A required a total of 24 operations from commercially available starting materials with the longest linear sequence being 21 steps.     

From a biogenetic scenario to a synthesis of the ABC ring of manzamine A

On the basis of a biogenetic proposal for explaining the biogenesis of manzamine A, the cycloaddition of dihydropyridinium salt 26 with diene derivative 5 leads to adducts 27. These adducts, as well as their related and previously described analogues 9, are now shown to be precursors of diene derivatives such as 10, 13, and 28. Treatment of diene 32 with sodium azide resulted in a one-step formation of the tricyclic imino derivative 34. This key intermediate was further transformed into tricyclic derivative 40, which possesses the essential features of the ABC ring of manzamine A.     

Antimalarial activity of a new family of analogues of manzamine A

Manzamine A represents an important lead structure for the development of novel antimalarial chemotherapies. The synthesis and biological evaluation of a group of simplified analogues of manzamine A, which were designed to examine the roles of the A and D rings and of both the relative stereochemistry and the orientation of the beta-carboline heterocycle on the antimalarial activity of manzamine A, are described. [structure: see text]     

The biocatalytic conversion of 8-hydroxymanzamine A to manzamine A

The selective dehydroxylation of 8-hydroxymanzamine A (1) to form manzamine A (2) can be completed by fermentation with Fusarium solani or Streptomyces seokies. This unique biocatalytic conversion is important due to the fact that manzamine A has more desirable biological activity when assayed in a murine model against malaria.     

Synthetic modification of manzamine A via Grubbs metathesis. Novel structures with enhanced antibacterial and antiprotozoal properties

A strategy for the structural modification of biologically important alkene-containing natural products via ring-opening olefin metathesis is described. Exposure of manzamine A 1 to the second-generation Grubbs catalyst in the presence of ethylene leads to the formation of 2 and 4. The antibacterial activity of the novel manzamine analogue 2 (IC50=0.10 nM) against Mycobacterium intracellulare is ca. 2-fold more potent than that of ciprofloxacin (IC50=0.18 nM), a drug that is frequently used against antibiotic-resistant infections.     

Enantioselective total synthesis of marine alkaloids,manzamine A and related compounds

A review of our studies toward the enantioselective total synthesis of ircinal A, manzamine A and related compounds is presented in detail.     

Manzamine B and C,two novel alkaloids from the sponge haliclona sp.

The title compounds were isolated from a marine sponge collected off Okinawa. Their structures were determined by X-ray and shown to be 1-β-carbolines. Manzamine C was the 2-ethyl-N-azacycloundec-6-ene derivative, whereas manzamine B was more complex being the epoxy isomer of the free base of dihydromanzamine A.     

New manzamine alkaloids with potent activity against infectious diseases.

The isolation of the new enantiomers of 8-hydroxymanzamine A (1), manzamine F (2), along with the unprecedented manzamine dimer, neo-kauluamine from an undescribed genus of Indo-Pacific sponge (family Petrosiidae, order Haplosclerida) is reported. The relative stereochemistry of neo-kauluamine was established through detailed analysis of NOE-correlations combined with molecular modeling. The significance of the manzamines as in vivo antimalarial agents with superior activity to the clinically used drugs artemisinin and chloroquine is discussed along with the activity in vitro against the AIDS-opportunistic infectious diseases tuberculosis and toxoplasmosis. Reexamination of the sponges identified as Prianos, and Pachypellina, in earlier publications has confirmed that these are members of the same genus as the sponge described here, but differ at the species level.     

Zamamidine C, 3,4-dihydro-6-hydroxy-10,11-epoxymanzamine A, and 3,4-dihydromanzamine J N-oxide, new manzamine alkaloids from sponge Amphimedon sp.

New manzamine alkaloids, zamamidine C (1), 3,4-dihydro-6-hydroxy-10,11-epoxymanzamine A (2), and 3,4-dihydromanzamine J N-oxide (3), have been isolated from an Okinawan marine sponge Amphimedon species. The structures and stereochemistries of 1-3 were elucidated from the spectroscopic data and chemical derivatization. Zamamidine C (1) is a new manzamine alkaloid possessing a second β-carboline ring via an ethylene unit at N-2 of manzamine D, while 3,4-dihydro-6-hydroxy-10,11-epoxymanzamine A (2) is the first manzamine alkaloid possessing an epoxide ring at C-10 and C-11. Zamamidine C (1) showed significant antitrypanosomal activity against Trypanosoma brucei brucei, the parasite associated with sleeping sickness, and antimalarial activity against Plasmodium falciparum, the causative agent of malaria in vitro.     

Total synthesis of haliclamine A, a macrocyclic marine alkaloid related to the key biogenetic intermediate of manzamines

The first total synthesis of haliclamine A (1), a macrocyclic marine alkaloid closely related to the key bisdihydropyridine intermediate 3 of the biogenetically unique manzamine family, has been efficiently achieved via stepwise inter- and intramolecular N-alkylations of 3-alkylpyridine derivatives 26 and 28.     

Synthetic study on efficient stereoselective construction of tricyclic core skeleton of manzamine A

Tricyclic core skeleton of manzamine A was constructed stereoselectively from the fused nitrogen-containing bicyclic enone 3 via a novel and efficient strategy including sequential stereoselective Diels-Alder reaction, Curtius rearrangement, and intramolecular lactam formation reaction.     

A new cyclostellettamine from sponge Amphimedon compressa

A new compound,8,8′-dienecyclostellettamine,was isolated from the marine sponge Amphimedon compressa.Its structure was elucidated by spectroscopic methods including ID and 2D NMR,UV,IR,ESI-MS,MALDI-MS techniques.It is probably an important precursor of the manzamine alkoids,and also showed vigorous antibacterial activities.     

The first total synthesis of nakadomarin A

(-)-Nakadomarin A is a member of manzamine alkaloid isolated from a marine sponge and have a unique hexacyclic structure. The first total synthesis of (+)-nakadomarin A, an enantiomer of natural product, has been accomplished from stereochemically defined 4-oxopiperidin-3-carboxylic acid derivative. The synthesis established the structure of nakadomarin A including absolute configuration.     

Synthetic study of manzamine B: synthesis of the tricyclic central core by an asymmetric Diels-Alder and RCM strategy

Tricyclic core of manzamine B was successfully synthesized through asymmetric Diels-Alder reaction and RCM strategy. Cr-salen-F complex was found to be the most effective catalyst in DA reaction of aminodienes with heterocyclic dienophiles to give up to 97% ee. In the construction of 11-membered ring by RCM, first-Grubbs cat. gave better stereoselectivity.     

Reductive amidation of nitroarenes: a practical approach for the amidation of natural products

A simple and practical approach for the one-pot conversion of nitroarenes into amide derivatives has been developed. Zinc and acetic acid are utilized as a reducing agent, and acyl chloride and triethylamine are used as the acylating agent in DMF with good yield (∼60%) of the amide. This method was applicable to manzamine A (1), where the yield of 6-cyclohexamidemanzamine A (7) was significantly improved (56%) by this approach relative to (17%) by beginning with the amine.     

Interaction of manzamine A with glycogen synthase kinase 3β: a molecular dynamics study

The search for the possible binding site of manzamine A to glycogen synthase kinase 3β(GSK-3β) was performed by molecular docking followed by molecular dynamics simulation and calculations of the Gibbs free energy of inhibitor—kinase binding. The cavity between the glycine-rich loop, the loop C, and the activation loop is the most likely site of interaction.