The total synthesis of (-)-crispatene

Synthetic study toward tridachiapyrone B

A convergent approach to the skeleton of tridachiapyrone B is described taking advantage of the desymmetrization of α,α'-dimethoxy-γ-pyrone leading to α-crotyl-α'-methoxy-γ-pyrone in one step. To construct the quaternary carbon of the 2,5-cyclohexadienone of the target, a strategy based on the Robinson-type annulation of an aldehyde derived from α-crotyl-α'-methoxy-γ-pyrone was applied. The grafting of the simplified target's side chain was demonstrated through an oxidative anionic oxy-Cope rearrangement of the tertiary alcohol arising from the 1,2-addition of a 1,3-dimethylallyl reagent to 2,5-cyclohexadienone connected to the α'-methoxy-γ-pyrone motif.

Modular Total Synthesis of iso-Archazolids and Archazologs

Full details on the design, development, and successful implementation of suitable synthetic strategies directed toward the total synthesis of iso-archazolids and archazologs are reported. Both a biomimetic and a multistep total synthesis of iso-archazolid B, the most potent and least abundant archazolid, are described. The bioinspired conversion from archazolid B was realized by a high-yielding 1,8-Diazabicyclo[5.4.0]undec-7-ene catalyzed one-step double-bond shift. A highly stereoselective total synthesis was accomplished in 25 steps, involving a sequence of highly stereoselective aldol reactions, an efficient aldol condensation to forge two elaborate fragments, and a challenging ring-closing metathesis macrocyclization with an unusual Stewart-Grubbs catalyst. These strategies proved to be generally useful and could be successfully implemented for the preparation of three novel iso-archazolids as well as five novel archazologs, lacking the thiazole side chain. A wide variety of further archazolids and archazologs may now be targeted for exploration of the promising anticancer potential of these polyketide macrolides.

Reassignment of crispatene, isolation and chemical characterization of stachydrine, isolated from the marine mollusk Elysia crispata

The molluscan genus Elysia Risso, 1818 (Sacoglossa) is composed of shell-less herbivore sea slugs. From these marine organisms, polyketides such as polypropynates have been isolated and showed cytotoxic, antibiotic, and antifungal, and antiviral properties. In this work, we reported the isolation, and structure elucidation of two compounds isolated from marine mollusk E. crispata. Both compounds isolated, crispatene (1) and stachydrine (2), were purified by HPLC. The chemical structure of compound (1) was reassigned through 1D and 2D NMR experiments and high-resolution electrospray ionization mass spectrometry (HRESIMS). On the other hand, this is the first time that compound (2) has been found in this species of mollusk or the marine environment, previously, (2) has only been found in terrestrial plants or bacteria in symbiosis with plants.

Biomimetic Total Synthesis of (±)-Carbocyclinone-534 Reveals Its Biosynthetic Pathway

Carbocyclinone-534 is a new antibiotic produced after the metabolism of tapinarof. We identify a biomimetic total synthesis of carbocyclinone-534 in eight steps by taking advantage of an intermolecular Diels-Alder homodimerization/dehydrogenation/intramolecular Diels-Alder cycloaddition cascade. This synthetic sequence provides direct experimental evidence for revealing the biosynthetic pathway of carbocyclinone-534.

A chiral auxiliary-based synthesis of the C5–C17 trans-decalin framework of anthracimycin

Intramolecular Diels–Alder [4 + 2] cycloaddition using a chiral Evans oxazolidinone auxiliary affords the trans-decalin framework of the potent antibiotic anthracimycin.

The iso-Nazarov reaction

The acid-promoted cycloisomerization of conjugated dienals and linearly-conjugated dienones for the synthesis of five-membered ring systems is reviewed.

Direct construction of vicinal all-carbon quaternary stereocenters in natural product synthesis

Molecules containing vicinal all-carbon quaternary stereocenters are found in many secondary metabolites, and they exhibit a variety of biological and pharmacological activities.

Biomimetic synthesis and structural reassignment of the tridachiahydropyrones

The biomimetic synthesis and structural reassignment of tridachiahydropyrone, tridachiahydropyrone B and tridachiahydropyrone C, isolated from mollusks of the order Sacoglossa, using a sequence of photochemical transformations from a common polyene precursor are described. These complex natural products may act as sunscreens for the producing organism, thus offering protection from harmful UV radiation and oxidative damage.

Shaping the polypropionate biosynthesis in the solar-powered mollusc Elysia viridis

Polypropionates that incorporate pyrones are a family of polyketides featuring the chemistry of a few marine molluscs capable of phototrophic CO(2) fixation as a result of storing viable symbiotic chloroplasts in their bodies. The role and origin of these molecules is poorly investigated, although the unusual biological activities and chemistry of these natural products have recently received renewed interest. Here, we report the results of in vivo studies on production of gamma-pyrone-containing polypropionates in the Mediterranean mollusc Elysia viridis. Biosynthesis of the metabolites in the sacoglossan is shown to proceed through condensation of eight intact C(3) units by polyketide synthase assembly. LC-MS and NMR spectroscopic studies demonstrate that the process involves a pyrone tetraene (10) as key intermediate, whereas the levels of the final polypropionates (6, 7 and 9) are related to each other and show a significant dependence upon light conditions.

Stereoselective Syntheses of the Bioactive Polypropionates Aureothin, N-Acetylaureothamine, and Aureonitrile

[reaction: see text] Concise total syntheses of the bioactive polypropionates aureothin, N-acetylaureothamine, and aureonitrile are described.

Stereoselective Synthesis of Cyercene A and the Placidenes

Members of a family of alpha-methoxy-gamma-pyrone-containing polypropionate natural products have been stereoselectively synthesized. Two key iodovinyl pyrone building blocks were coupled to appropriately selected vinyl stannanes to assemble the highly substituted polyene side chains of the natural products. [structure: see text]

Biomimetic synthesis of (±)-9,10-deoxytridachione

A tandem Suzuki-coupling/electrocyclisation reaction sequence was employed for the biomimetic synthesis of (+/-)-9,10-deoxytridachione.