The first synthesis and absolute configuration of glaucescenolide

The first synthesis of glaucescenolide (1), a cytotoxic sesquiterpene isolated from the liverwort, Schistochila glaucescens, was achieved by starting from 2,2,6-trimethylcyclohexanone (2). The absolute configuration of the naturally occurring 1 was confirmed as 5S,7S,10R.     

An enantioselective synthesis and the absolute configuration of natural pumiliotoxin-C. Preliminary communication

(?)-Pumiliotoxin-C-hydrochloride, as well as its unnatural enantiomer, have been synthesized in an enantioselective manner starting from (S)- or (R)-norvaline, respectively. In the crucial cycloaddition step 11 → 12 (cf. scheme 2) the chiral center of 11 controls to a major extent the three developing centers of chirality. This synthesis shows unambigously the (2S)-configuration of natural pumiliotoxin-C.     

First enantioselective synthesis and determination of the absolute configuration of natural (+)-dehydro-β-monocyclonerolidol

The enantioselective synthesis and determination of the absolute configuration of (+)-dehydro-β-monocyclonerolidol, a natural product isolated from the liverwort P. subobtusa, has been achieved starting from (+)-karahana lactone as an enantiopure building block. Furthermore, the methodology applied provided a new approach towards the known (+)-γ-cyclohomocitral, a key intermediate in the sequence, and natural (+)-pallescensone.     

Vanchrobactin: absolute configuration and total synthesis

The stereochemistry of vanchrobactin, a siderophore produced by the bacterial fish pathogenVibrio anguillarum serotype O2, was elucidated by chiral capillary electrophoresis analysis and total synthesis as N-[N′-(2,3-dihydroxybenzoyl)-d-arginyl]-l-serine.     

Establishing the absolute configuration of the asbestinins: enantioselective total synthesis of 11-acetoxy-4-deoxyasbestinin D

A highly stereoselective synthesis of 11-acetoxy-4-deoxyasbestinin D (1) has been completed in 26 linear steps. The synthesis hinges on a selective glycolate aldol addition to establish the C-2 stereocenter, a ring-closing metathesis reaction to complete the oxonene, and an intramolecular Diels-Alder cycloaddition to establish the relative configuration at C-1, C-10, and C-14. This initial total synthesis of an asbestinin also serves to confirm the absolute configuration of this subclass of the C-2-C-11-cyclized cembranoid natural products.     

The first total synthesis of xenitorins B and C: assignment of absolute configuration

Starting from (-)-beta-pinene, the first total synthesis of xenitorins B and C has been accomplished, which also allowed the assignment of their absolute configuration.     

Radicamines A and B: synthesis and revision of the absolute configuration

[reaction: see text] Starting from D-xylose, enantioselective syntheses of 1 and 2, the proposed structures for radicamines A and B, were accomplished. Both (1)H and (13)C NMR spectra of 1 and 2 were identical with those of the natural products, but the optical rotation measurements identified that 1 and 2 were actually the enantiomers of the natural radicamines A and B, respectively.     

The first total synthesis of putaminoxin and determination of its absolute configuration

Asymmetric synthesis of putaminoxin, a phytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. Absolute configuration of putaminoxin was concluded to be 1 from comparison of the NMR data and [α]_D values of synthetic and natural putaminoxin.     

First enantioselective total synthesis of neocarazostatin B, determination of its absolute configuration and transformation into carquinostatin A

The first enantioselective total synthesis of neocarazostatin B, the determination of its absolute configuration and transformation into carquinostatin A are described.     

The first total synthesis and determination of the absolute configuration of chapecoderin A, B and C

The seco- and rearranged-labdanes, chapecoderins A 1, B 2, and C 3 have been synthesized for the first time starting from (S)-(+)-Wieland-Miescher ketone analogue 11. Their absolute configurations have been determined as depicted in the structures 1, 2 and 3.     

The first enantiospecific synthesis of (−)-heritol: absolute configuration determination

The first enantiospecific synthesis of (−)-heritol, from naturally occurring (R)-(+)-citronellal and confirmation of its absolute configuration, is described.     

Total synthesis of amphidinolactone A and its absolute configuration

Asymmetric synthesis of amphidinolactone A, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. Absolute configuration of amphidinolactone A was concluded to be 1 from comparison of the NMR data and [α]_D values of synthetic and natural amphidinolactone A.     

Verticilide: elucidation of absolute configuration and total synthesis

Verticilide (1) is a 24-membered cyclic depsipeptide isolated from the culture broth of Verticillium sp. FKI-1033. It inhibits ryanodine binding to ryanodine receptor (RyR) and has insecticidal activity. The stereochemistry of 2-hydroxyheptanoic acid in verticilide was elucidated by chiral HPLC analysis of the degradation product 6 and synthetic (+) and (-)-6. We also describe the practical total synthesis of verticilide. [reaction: see text].     

Determination by enantioselective synthesis of the absolute configuration of CPE, a potential intermediate in coronatine biosynthesis

The first enantioselective synthesis of the methyl ester of CPE, a potential intermediate in coronatine (COR) biosynthesis, is described. Comparison of the specific rotation of the synthetic ester with that of the methyl ester of natural CPE established that the latter possesses the (R) configuration. This configuration is the same as that found at the corresponding asymmetric center of coronatine. Structure: see text.     

An enantioselective total synthesis of (+)- and (-)-saudin. Determination of the absolute configuration.

A short efficient enantioselective synthesis of both (+)- and (-)-saudin, a naturally occurring hypoglycemic diterpene, is described. This synthesis establishes the absolute configuration of natural (-)-saudin for the first time. The key steps include the enantioselective construction of a dimethyl Hagemann's ester by an asymmetric Michael reaction and establishment of the key 1,3 disposed quaternary centers by means of a novel Ti(IV) promoted Claisen rearrangement. The assembly of the polycyclic ketal skeleton was likely under kinetic control proceeding via formation of the C1oxygen-C7 bond through an oxonium ion intermediate in the final stage.