Investigation into the absolute stereochemistry of the marine sponge alkaloid pyrinodemin A

The absolute configuration of the marine sponge alkaloid pyrinodemin A is established by organic synthesis.     

Enantioselective total synthesis of pyrinodemin A

Pyrinodemin A 1, a cytotoxic marine alkaloid, was synthesized in a convergent and enantioselective fashion. The key steps are an asymmetric intramolecular dipolar cycloaddition of an oxazoline N-oxide to introduce the bicyclic ring system of the molecule, a cuprate coupling for the extension of the saturated chain and a B-alkyl Suzuki coupling for the introduction of a 3-pyridyl moiety. Reductive amination allowed the coupling of the second side-chain onto the nitrogen atom to give 1. Additionally, attempts to prepare 1 from a trienic precursor by a double B-alkyl Suzuki reaction are described.     

Formal total synthesis of the cytotoxic marine ascidian alkaloid haouamine A

[reaction: see text] Described is a convergent 13-step synthesis of a pentacyclic compound which has previously been transformed into haouamine A, therefore constituting a formal total synthesis of this unique marine alkaloid.     

Model studies toward the total synthesis of the Lycopodium alkaloid spirolucidine

[reaction: see text] A strategy for the synthesis of the spirocyclic core of spirolucidine was explored through a model study. The diene 4a was prepared and photolyzed to give the desired [2 + 2] photoadduct 17 containing the correct relative stereochemistry corresponding to spirolucidine.     

Studies toward the total synthesis of nominine

The construction of the hetisane group of alkaloids, of which the extensively bridged nominine 17 is the simplest member, poses the ultimate challenge for those interested in the synthesis of the C20 diterpene alkaloids. We describe the synthesis of an advanced intermediate toward this goal. The key steps include reductive acylation, reductive deoxygenation, Birch reduction, and an intramolecular Lewis acid-catalyzed 1,6-addition of a carbamate to a dienone.     

Studies toward the total synthesis of clavulactone

Synthetic studies directed toward a total synthesis of clavulactone are reported. In light of the analysis made in our previous work, cyclopentane 4a (a key intermediate in the present work) was synthesized through a radical-mediated ring closure of a rationally designed substrate 25. Using HWE reactions, the lower and upper side-chains of 4a were converted into an allyl chloride and an allyl cyanohydrin, respectively. Subsequent treatment of the allyl chloride/cyanohydrin in a highly diluted THF solution with sodium bis(trimethylsiliyl)amide led to intramolecular alkylation and thus completed a major endeavor in synthesizing the dolabellane framework, construction of the eleven-membered ring. SmI(2)-mediated lactonization as a model reaction for the formation of the alpha,beta-unsaturated delta-lactone segment of clavulactone is also described.     

Total synthesis of the cytotoxic alkaloid luotonin A

The structure of luotonin A was unambiguously confirmed by total synthesis. Deprotonation of 3-oxo-1H-pyrrolo[3,4-b]quinoline gave an anion which was coupled with 2-sulfinylaminobenzoyl chloride (prepared by reaction of anthranilic acid with thiolyl chloride) to afford the natural product in 85 % yield.     

Studies toward the total synthesis of the hirsutellones

A strategy of tandem ketene-trapping/IMDA toward the total synthesis of the hirsutellones was attempted. The AB ring moiety of the hirsutellones was constructed with the proper stereochemistry.     

A total synthesis of the alkaloid deplancheine

The indole alkaloid deplancheine (1) has been synthesised utilising a Witting reaction on the octahydro[2,3-a]quinolizin-2-one (2) itself available in four synthetic steps from readily available materials.     

Studies toward the total synthesis of Wiedemannic acid

[reaction: see text] We report a novel and efficient diastereoselective synthesis of wiedemannic acid analogue 30 in 16 steps from 7 using a tandem oxy-Cope/Claisen/ene reaction as the key step. Comparison of NMR data between wiedemannic acid (1) and analogue 30 leads us to believe that the reported stereochemistry at the ring junction of 1 is incorrect.     

Studies toward the total synthesis of nagelamide K

A stereocontrolled strategy toward the synthesis of nagelamide K has been developed. The dimeric imidazole acrylate, diimidazolidenesuccinate, was constructed as a synthetic precursor by a Ni-catalyzed coupling reaction; the microwave-promoted intramolecular aza-Michael addition afforded the imidazo[1,5-a]pyridine core structure of nagelamide K in high stereoselectivity. A detaurine-dediamino analogue of nagelamide K has been prepared.     

A short biomimetic synthesis of marine sponge alkaloid Pyrinadine A

The biomimetic synthesis of the marine sponge alkaloid Pyrinadine A, based on the oxidative dimerisation of hydroxylamine, is reported.     

Studies toward the total synthesis of axinellamine and massadine

Intramolecular Diels-Alder reactions of several N-O linked 4-vinylimidazole dimers provide the expected adduct in moderate to good yield as a single, all trans stereoisomer, along with smaller amounts of the inverse electron demand adduct. Oxidative rearrangement of the cycloadducts occurs on treatment with Davis' reagent, providing a single spiro imidazolone in good yield and with excellent levels of stereocontrol albeit epimeric at the spiro center found in axinellamine and massadine.     

A chemoenzymatic total synthesis of the Amaryllidaceae alkaloid narseronine

A 15-step and fully stereocontrolled total synthesis of the title alkaloid 1 has been accomplished using the enantiomerically pure and enzymatically-derived cis-1,2-dihydrocatechol 2 as starting material. The final and pivotal step involved the intramolecular hetero-Michael addition of secondary amine 16 to a tethered enone moiety followed by trapping of the resulting enolate through its reaction with an adjacent ester residue.     

A formal total synthesis of the marine alkaloid aaptamine

A new strategy for the synthesis of benzo[de][1,6]naphthyridine derivative 2,3,3a,4,5,6-hexahydroaaptamine, which involves the construction of the isoquinoline ring after elaboration of the quinoline moiety, is described. Since 2,3,3a,4,5,6-hexahydroaaptamine has been previously synthesized as a key intermediate en route to the marine alkaloid aaptamine, access to this compound represents a formal total synthesis of the natural product.     

Studies toward the total synthesis of vinigrol. synthesis of the octalin ring

[reaction: see text] Herein, we disclose our results regarding various strategies toward the assembly of the octanyl ring of vinigrol. Attempts to generate the problematic eight-membered ring through a ring expansion or via unification of the terminal olefins using the ring-closing metathesis were not successful. The cyclooctane ring was created via a sequential hydroxy Diels-Alder/Claisen rearrangement reaction of diene 55 and N-benzylmaleimide.     

Studies toward the total synthesis of gymnocin A,a cytotoxic polyether: a highly convergent entry to the F-N ring fragment

[structure: see text] An efficient and highly convergent synthesis of the FGHIJKLMN ring fragment of gymnocin A, a cyctotoxic polycyclic ether isolated from the notorious red-tide forming dinoflagellate Gymnodinium mikimotoi, has been achieved. The present synthesis relied on extensive use of the B-alkyl Suzuki-Miyaura coupling reaction.     

Total synthesis of the cytotoxic alkaloid 22-hydroxyacuminatine

The total synthesis of the cytotoxic alkaloid 22-hydroxyacuminatine has been achieved in 14.9% overall yield starting from 2-methylcinnamic acid via the key intermediate 5-ethoxymethylisoquinolin-1-one.     

Studies toward the total synthesis of garsubellin A: a concise synthesis of the 18-epi-tricyclic core

[reaction: see text] During studies directed toward the total synthesis of garsubellin A, a concise stereocontrolled synthesis of the 18-epi-tricyclic compound 3 was achieved. Key steps were a one-pot stereoselective construction of the bicyclic lactone 23 followed by a formal migration to the bicyclo[3.3.1]nonane-1,3,5-trione and an intramolecular Wacker-type tetrahydrofuran ring formation.