Absolute stereochemistries and total synthesis of (+)-arisugacins A and B, potent, orally bioactive and selective inhibitors of acetylcholinesterase

Efficient and stereoselective synthesis of sugar fused pyrano[3,2-c]pyranones as anticancer agents

A highly stereoselective, efficient and facile route was achieved for the synthesis of novel and biochemically potent sugar fused pyrano[3,2-c]pyranone derivatives starting from inexpensive, naturally occurring d-galactose and d-glucose. First, β-C-glycopyranosyl aldehydes were synthesized from these d-hexose sugars in six steps, with overall yields 41-55%. Next, two different 1-C-formyl glycals were synthesized from these β-C-glycopyranosyl aldehydes by treatment in basic conditions. The optimization of reaction conditions was carried out following reactions between 1-C-formyl galactal and 4-hydroxycoumarin. Next, 1-C-formyl galactal and 1-C-formyl glucal were treated with nine substituted 4-hydroxy coumarins at room temperature (25 °C) in ethyl acetate for ∼1-2 h in the presence of l-proline to obtain exclusively single diastereomers of pyrano[3,2-c]pyranone derivatives in excellent yields. Four compounds were found to be active for the MCF-7 cancer cell line. The MTT assay, apoptosis assay and migration analysis showed significant death of the cancer cells induced by the synthesized compounds.

Anti-Insect Properties of Penicillium Secondary Metabolites

In connection with their widespread occurrence in diverse environments and ecosystems, fungi in the genus Penicillium are commonly found in association with insects. In addition to some cases possibly implying a mutualistic relationship, this symbiotic interaction has mainly been investigated to verify the entomopathogenic potential in light of its possible exploitation in ecofriendly strategies for pest control. This perspective relies on the assumption that entomopathogenicity is often mediated by fungal products and that Penicillium species are renowned producers of bioactive secondary metabolites. Indeed, a remarkable number of new compounds have been identified and characterized from these fungi in past decades, the properties and possible applications of which in insect pest management are reviewed in this paper.

Bio-inspired formal total synthesis of (±)-bisabosqual A

A new approach was developed to construct a hexahydrobenzofurobenzopyran ring system by an oxa-[3+3], Diels–Alder reaction and oxidative aromatization. As a synthetic application, the bio-inspired formal synthesis of bisabosqual A was achieved.

Total synthesis of (±)-(1β,4β,4aβ,8aα)-4,8a-dimethyl-octahydro-naphthalene-1,4a(2H)-diol

The first total synthesis of (±)-(1β,4β,4aβ,8aα)-4,8a-dimethylocta-hydronaphthalene-1,4a(2H)-diol (1), a degraded sesquiterpene isolated from a fermentation broth of Streptomyces albolongus, has been achieved via three different synthetic approaches (13–15 steps) starting from racemic Wieland–Miescher ketone (2).

Stereoselective synthesis of carbohydrate fused pyrano[3,2-c]pyranones as anticancer agents

Efficient synthesis of pyrano[3,2-c]pyranones motif as fused carbohybrids and their anticancer activities reported.

A computational view on the significance of E-ring in binding of (+)-arisugacin A to acetylcholinesterase

A computational docking study of a series of de novo structural analogs of the highly potent, non-nitrogen containing, acetylcholinesterase inhibitor (+)-arisugacin A is presented. In direct comparison to the recently reported X-ray single-crystal structure of (+)-territrem B bound hAChE, the modeling suggests that there is a unique conformational preference for the E-ring that is responsible for the superior inhibitory activity of (+)-arisugacin A against hAChE relative to (+)-territrem B, and that substitutions on the E-ring also play an important role in the protein-ligand interaction.

Territrem and butyrolactone derivatives from a marine-derived fungus Aspergillus terreus

Seventeen lactones including eight territrem derivatives (1–8) and nine butyrolactone derivatives (9–17) were isolated from a marine-derived fungus Aspergillusterreus SCSGAF0162 under solid-state fermentation of rice. Compounds 1–3 and 9–10 were new, and their structures were elucidated by spectroscopic analysis. The acetylcholinesterase inhibitory activity and antiviral activity of compounds 1–17 were evaluated. Among them, compounds 1 and 2 showed strong inhibitory activity against acetylcholinesterase with IC₅₀ values of 4.2 ± 0.6, 4.5 ± 0.6 nM, respectively. This is the first time it has been reported that 3, 6, 10, 12 had evident antiviral activity towards HSV-1 with IC₅₀ values of 16.4 ± 0.6, 6.34 ± 0.4, 21.8 ± 0.8 and 28.9 ± 0.8 μg·mL⁻¹, respectively. Antifouling bioassay tests showed that compounds 1, 11, 12, 15 had potent antifouling activity with EC₅₀ values of 12.9 ± 0.5, 22.1 ± 0.8, 7.4 ± 0.6, 16.1 ± 0.6 μg·mL⁻¹ toward barnacle Balanus amphitrite larvae, respectively.

One-pot five-component synthesis of spirocyclopenta[b]chromene derivatives and their acid-catalyzed rearrangement

The reaction of the zwitterionic intermediate, generated in situ from either tert-butylisocyanide or cyclohexylisocyanide and acetylenedicarboxylates, with 3-cyanochromones is described, whereupon spirochromenofuran derivatives 5 or 6 were obtained in good yields. The subsequent acid-catalyzed rearrangement of the isolated 2-imino-spirochromenofurans 5 to 2-amino-spirochromenofurans 7 has also been studied. Rational mechanistic schemes for the formation of compounds 5, 6, and 7 are proposed. The structure elucidation of the products was accomplished by 1D and 2D NMR experiments and confirmed by X-ray crystallographic analysis. Full assignment of all (1)H and (13)C NMR chemical shifts has been unambiguously achieved with the aid of DFT/GIAO calculations.

Constructing the Architecturally Distinctive ABD-Tricycle of Phomactin A through an Intramolecular Oxa-[3 + 3] Annulation Strategy

Our efforts in constructing the ABD-ring of phomactin A through an intramolecular oxa-[3 + 3] annulation strategy is described. This struggle entailed finding a practical and efficient preparation of annulation precursor, and a realization of the unexpected competing regioisomeric pathway. The success entailed accessing the A-ring through Diels-Alder cycloaddition of Rawal's diene. Furthermore, the discovery that the regioisomers from the annulation existed as atropisomers with respect to the D-ring olefin and that they could be equilibrated to the desired ABD-tricycle, allowing large quantities of tricycle to be accessed.

Total synthesis of (±)-phomactin A. Lessons learned from respecting a challenging structural topology

Our struggles and ultimate success in achieving a total synthesis of phomactin A are described. Our strategy features an intramolecular oxa-[3 + 3] annulation to construct its unique ABD-tricyclic manifold. Although the synthesis would constitute a distinctly new approach with the 12-membered D-ring of phomactin A being assembled simultaneously with the 1-oxadecalin at an early stage, the ABD-tricycle represents a unique structural topology that would pose a number of unprecedented challenges. One challenge concerned elaborating this tricycle to have oxygenation at the proper carbon atoms. To overcome this, we would utilize a Kornblum-DeLaMare ring-opening of a peroxide bridge as well as a challenging late-stage 1,3-allylic alcohol transposition. Further, the structural intricacies of the ABD-tricycle were uncovered by a conformational analysis that would be critical for the C5a-homologation.

(+)-Arisugacin A--computational evidence of a dual binding site covalent inhibitor of acetylcholinesterase

A computation docking study of the highly potent, non-nitrogen containing, acetylcholinesterase inhibitor (+)-arisugacin A is presented. The model suggests that (+)-arisugacin A is a dual binding site covalent inhibitor of AChE. These findings are examined in the context of Alzheimer's disease-modifying therapeutic design. (+)-Arisugacin A's revealed mode of action is unique, and may serve as a basis for the development of AD therapeutics capable of treating the symptomatic aspects of AD, while being neuroprotective with long term efficacy.

Total synthesis of phomactin A

A total synthesis of (+/-)-phomactin A is described to highlight the final completion of a complex natural product target that had commenced with an intramolecular oxa-[3 + 3] annulation strategy in the construction of the ABD-tricycle. These efforts reveal structural intricacies of this ABD-tricycle with an illustrative example being the conformational analysis that was ultimately critical for the C5a-homolgation.

An Enantioselective Synthesis of the ABD Tricycle for (-)-Phomactin A Featuring Rawal's Asymmetric Diels-Alder Cycloaddition

An enantioselective synthesis of the ABD-ring of (-)-phomactin A is described here. The sequence features Rawal's asymmetric Diels-Alder cycloaddition. The overall length is significantly reduced from our previous attempt.

Tetracyclic terpenoids from Dasyscyphus niveus, dasyscyphins D and E

Cultures of the ascomycete Dasyscyphus niveus have yielded two new tetracyclic dasyscyphin-type terpenoids (1 and 2), and their structures were elucidated by NMR spectroscopy and X-ray crystallography. The absolute configuration of dasyscyphin D (1) was determined by synthesis and NMR spectroscopy of diastereomeric MTPA esters. Both compounds inhibited the germination of conidia of Magnaporthe grisea at 25 microg/mL.

Efficient total synthesis of novel bioactive microbial metabolites

Bioactive natural products produced by microbes have almost limitless potential in pharmaceutical applications, and the organic synthesis of such products as lead compounds will result in the creation of new and widely useful pharmaceutical products. A program of discovery of naturally occurring bioactive microbial metabolites has been ongoing at the Kitasato Institute. We have also developed efficient, rational, and highly flexible production methods for generation of target compounds, synthesis of related compounds, elucidation of their structure-activity relationships, and the possible creation of improved bioactive compounds. In this Account, the isolation and total synthesis of naturally occurring bioactive microbial metabolites in order to create novel medicines for specific illnesses is described. This covers diseases and conditions such as atherosclerosis, Alzheimer's disease, cancer, inflammation, and osteoporosis, among others, and focuses on six specific compounds. Pyripyropenes were discovered from Aspergillus fumigatus FO-1289 through our screening of microbial metabolites that strongly inhibit acyl-CoA cholesterol acyltransferase (ACAT) in order to develop a new class of cholesterol-lowering agents. These novel polyoxygenated mixed polyketide-terpenoid (meroterpenoid) metabolites contain a fused pyridyl alpha-pyrone moiety. We carried out the first total synthesis of (+)-pyripyropene A via a flexible, concise, and highly efficient route and also clarified the structure-activity relationships. Arisugacins were discovered from Penicillium sp. FO-4259 by our screening of microbial metabolites that strongly inhibit acetylcholinesterase (AChE) in order to create novel medicines for Alzheimer's disease (AD). Arisugacins are also meroterpenoids. We have achieved the first convergent total synthesis of arisugacins A and B. Lactacystin was isolated from Streptomyces sp. OM-6519 via our screening of microbial metabolites that promote the differentiation of the neuroblastoma cell to further discover new AD medicines. Lactacystin has a novel gamma-lactam thioester structure and is also a selective and strong proteasome inhibitor. We have developed a concise approach to synthesize lactacystin designed to afford easy access to the original compound and a variety of analogs. Macrosphelides were isolated from Microsphaeropsis sp. FO-5050 from our screening of microbial metabolites that inhibit the adhesion of HL-60 cells to human umbilical vein endothelial cells (HUVEC). Macrosphelides are the first 16-membered macrotriolides. Macrosphelides prevent cell-cell adhesion by inhibiting the binding of sialyl Lewis X to E-selectin. We have accomplished the first efficient total synthesis of macrosphelides. Madindolines were isolated from Streptomyces nitrosporeus K93-0711 by our program to discover new interleukin 6 (IL-6) modulators. Madindolines are comprised of a 3a-hydroxyfuroindoline ring connected at nitrogen via a methylene bridge to a cyclopentene-1,3-dione ring. We have developed an efficient and practical total synthesis of madindolines. Madindoline A binds to gp130 selectively and inhibits IL-6 activity. Neoxaline was isolated from Aspergillus japonicus Fg-551. Neoxaline is a member of a novel class of biologically active indole alkaloids characterized by a unique indoline spiroaminal framework and binds to tubulin, which results in inhibition of tubulin polymerization. We have developed a concise stereoselective synthesis of the indoline spiroaminal framework of neoxaline.

Diastereoselective annulation of 4-hydroxypyran-2H-ones with enantiopure 2,3-dideoxy-α,β-unsaturated sugar aldehydes derived from respective glycals

One-pot condensations of 4-hydroxypyran-2H-ones 1 and 2, respectively, with various enantiopure 2,3-dideoxy-alpha,beta-unsaturated carbohydrate enals in the presence of l-proline in EtOAc at room temperature generated pyrano-pyrones. It was observed that, while benzyl-protected carbohydrate enals on condensation with 1 or 2 under the above conditions produced an inseparable diastereomeric mixture in a ratio of 1:1, the acyl-protected carbohydrate enals on treatment with 1 or 2 under identical conditions yielded products with moderate to very high diastereoselectivity. A remarkable asymmetric induction was noticed from the C-4 stereogenic center of the acyl-protected carbohydrate enals. An almost complete diastereoselectivity was observed in those reactions that involved condensation of 1 with acetyl-protected enals 5 and 7. The reaction of 2 with 5 also proceeded diastereoselectively to furnish the corresponding annulated product. The reaction presumably took place by C-1,2-addition of the pyrone onto the iminium salt of the alpha,beta-unsaturated carbohydrate enal generated in situ, followed by beta-elimination and cyclization of the 1-oxatriene involving a 6pi-electron electrocyclic process to yield a 2H,5H-pyrano[3,2-c]pyran-5-one derivative.

Unique structural topology and reactivities of the ABD tricycle in phomactin A

Stereoselective and transannular reactivities are described for the ABD tricyclic manifold of phomactin A that possesses a unique structural topology.