Total synthesis of naturally occurring 5,6,7- and 5,7,8-trioxygenated coumarins

The synthesis of five naturally occurring polyoxygenated coumarins is described. It concerns two 5,6,7-trioxygenated coumarins, i.e., 6-hydroxy-5,7-dimethoxycoumarin (fraxinol) 1 and 5,6,7-trimethoxycoumarin 2, and three 5,7,8-trioxygenated coumarins, i.e., 8-hydroxy-5,7-dimethoxycoumarin (leptodactylone) 3, 5,7,8-trimethoxycoumarin 4 and 8-(3-methyl-2-butenyloxy)-5,7-dimethoxycoumarin (artanin) 5. Key feature of the synthetic pathway is the synthesis of suitable tetraoxygenated benzaldehydes, which are then converted to the corresponding coumarins via a Wittig reaction.     

Carbocyclization of d-glucose: syntheses of gabosine I and streptol

d-Glucose was differentially protected with a trans-diacetal at C-2,3, an ethoxymethyl ether at C-4, and a tert-butyldimethylsilyl ether at C-6, and then carbocyclized via a key Horner-Wadsworth-Emmons (HWE) olefination to give a versatile synthetic intermediate, enone 13, which was readily transformed into gabosine I and streptol.     

First asymmetric synthesis of both enantiomers of andirolactone

We have achieved the first asymmetric synthesis of (+)- and (−)-andirolactone. The key steps were separation of limonene oxide diastereomers, asymmetric oxidation induced by the chiral intermediate and ring-closing metathesis in the presence of catalytic amounts of Lewis acid to form the spirocyclic butenolides.     

Synthetic studies on amphidinolides C and F: synthesis of the C18-C29 segment of amphidinolide F

The C18-C29 segment of amphidinolide F is synthesised in 12 steps from 1,4-butanediol. Key steps include a mono-Sharpless dihydroxylation of a dienoate, iodocyclisation to construct the trans-THF ring and an E-selective Wittig reaction to introduce the C25-C26 olefin.     

Total synthesis of pteridic acids A and B

A convergent synthesis of pteridic acids A and B, epimeric spiroacetal polyketides with potent plant growth promoter properties, is described. The use of boron aldol methodology efficiently achieved the stereocontrolled construction of advanced C1-C11 and C12-C16 subunits, which were coupled to generate a linear (Z)-enone precursor that underwent spiroacetalization with HF·pyridine, providing pteridic acids A and B after saponification.     

An efficient, economical synthesis of hydroxytyrosol and its protected forms via Baeyer-Villiger oxidation

An efficient and practical preparation of hydroxytyrosol and its orthogonally-protected forms was developed from inexpensive tyrosol. The utilization of Baeyer-Villiger oxidation enables the chemoselective introduction of a phenolic hydroxyl group in good yield.     

Studies towards the total synthesis of Phostriecin

A synthetic approach toward the phostriecin, an antitumor natural product is described. The key features of the present synthesis are Wittig reaction, synthesis of homoallylic alcohol using Brown’s protocol (alkoxyallylboration) and RCM for the creation of unsaturated lactone moiety of phostriecin.     

A fast and straightforward route towards the synthesis of the lissoclimide class of anti-tumour agents

The synthesis of the chiral core structure of the lissoclimide class of anti-tumour agents containing three rings, including a chiral succinimide subunit and an exocyclic double bond, has been investigated. The compound 7 was obtained, without the use of any protecting groups for the alcohol at C-12, via an asymmetric boron-mediated aldol addition as the key step to install the chiral centres of the rare succinimido methanol moiety. This was followed by a sequence of lactonisation, microwave-assisted amidation and imidation reactions.     

Stereoselective total synthesis of C2-symmetric natural products pyrenophorol and its derivatives

Abstract

A stereoselective total synthesis of 16-membered C₂-symmetric macrodiolide Pyrenophorol, Tetrahydropyrenophorol and 4,4-diacetylpyrenophorol have been accomplished. The synthesis started from commercially available L-Aspartic acid and the key reactions involved are regioselective epoxide opening, CBS reduction, Pinnick oxidation and Mitsunobu dilactonization.     

A convenient synthesis of olefins via deacylation reaction

A convenient and environmentally-friendly synthetic method of olefins via deacylation reaction is described. The reaction gives olefins by condensation of aldehydes with a variety of 1,3-dicarbonyl compounds in the presence of anhydrous potassium carbonate at room temperature in high yields (70-90%) in one step. The synthetic potential of this strategy can be used as an alternative procedure to the Wittig, Wittig-Horner reactions. The stereochemistry of the resulted olefins was determined by NOE experiment with correct radio frequency and X-ray analysis. The E/Z selectivity of the deacylation reaction depends on the α-substituents of the 1,3-dicarbonyl compounds.     

A simple and efficient synthesis of (±)-mesembrine

A simple and efficient synthesis of (±)-mesembrine 1 is described employing double Michael addition and as the key step in 18% overall yield.     

A total synthesis of 11-O-methyldebenzoyltashironin

A concise total synthesis of 11-O-methyldebenzoyltashironin is reported in which oxidative dearomatization-IMDA-RCM triad constitutes the key ring forming steps, while an unorthodox DIBAL-H mediated stereo- and regioselective reductive epoxide openings and implementation of the vinyl bromide-carbonyl equivalency concept were pivotal to the success of this endeavor.     

Total synthesis of farylhydrazones A and B

Herein we report a concise total synthesis of farylhydrazones A and B, naturally occurring phenylhydrazones recently isolated from cultures of the Cordyceps-colonizing fungus Isaria farinosa, completed in six and five steps respectively starting from 2-nitrobenzoic acid. The synthesis is completely scalable, and highly convergent—making it adaptable for the preparation of analogues and investigation into the biological activity of these unique natural products.     

Total syntheses and absolute stereochemistry of decarestrictines C1 and C2

The total syntheses of decarestrictines C₁ and C₂ have been described. The synthetic strategy involves a practical and flexible approach using esterification and ring-closing metathesis to unite the acid and alcohol fragments. The acid fragments are enantiomers of each other and have been prepared from l-(−)-malic acid via similar transformations; in Sharpless asymmetric epoxidation, (+)-DET has been used for decarestrictine C₁ and (−)-DET for decarestrictine C₂. The alcohol fragment is identical for both decarestrictines C₁ and C₂ and has been accessed from d-(+)-mannitol. Comparison of the ¹H and ¹³C NMR data combined with the computational studies predicts the presence of two conformations without and with hydrogen bonding (conformational isomers I and II for decarestrictine C₁), respectively. The ¹H and ¹³C NMR data for decarestrictine C₂ completely agreed with the analytical data reported by Kibayashi et al.     

A straightforward synthesis of glyco-2,7- and 2,8-dienes

In this paper, we report the efficient preparation of carbohydrate-derived 2,7- and 2,8-dienes. By our synthetic approach, we have quickly converted d-glucose 1 to (E)-ethyl-2,3-dideoxy-d-gluco-oct-2-enoate 5, which led to the desired (E)-ethyl-9,9-dibromo-2,3,8,9-tetradeoxy-4,5,6,7-tetra-O-trimethylsilyl-d-gluco-nona-2,8-dienoate 19 with satisfying yield.     

Scalable total synthesis of (-)-berkelic acid by using a protecting-group-free strategy

Supply chain: the polycyclic core of (-)-berkelic acid (1) was constructed in just one step from very simple starting materials. The total synthesis of 1 involves a seven-step linear sequence. Protection/deprotection steps were avoided and all but the last step were performed on a gram scale. This synthesis could solve the supply problem associated with the exhaustion of the natural source.     

A concise synthesis of honokiol

Two approaches to the synthesis of the plant-derived biaryl neolignan honokiol are described. The second approach provided the natural product in either four steps with 34% overall yield or five steps and 55% overall yield.     

The discovery, isolation, elucidation of structure, and synthesis of antamanide

Antamanide is the name we have given to a constituent of the fungus Amanita phalloides. This substance counteracts the lethal action of the Amanita toxins phalloidine and α-amanatine if administered to the white mouse before, or simultaneously with, the poisons. Its concentration in the fungus is, however, so low that the toxic action of the latter predominates. Antamanide is a cyclic decapeptide formed from the L -amino acids alanine, phenylalanine, proline, and valine in the molar ratio 1:4:4:1. The amino-acid sequence was determined by a combination of gas chromatography and mass spectrometry. The structural formula assigned was confirmed by synthesis according to a classic route of peptide chemistry.