Aristoserratenine and tasmanine: structures and absolute configurations

The structure of the Aristorelia alkaloid aristoserratenine ($\text{1}$) has been determined by spectroscopic means, and confirmed by rearrangement to aristoteline ($\text{2}$). The structure of tasmanine ($\text{3}$) has been confirmed similarly, and the configuration at the spiro carbon of each base has been determined by nOe experiments.     

Enantioselective synthesis and absolute configurations of aculeatins A and B

The two naturally occuring, bioactive spiroacetals aculeatins A and B have been synthesized for the first time in enantiopure form using an asymmetric allylation as the only chirality source. A further key step was a stereoselective aldol reaction with remote induction. The absolute configurations of the natural products have been established and the previously assigned relative configurations have been corrected.     

Revision of the absolute configurations of bethosides B and C and their aglycone

The absolute stereochemistry of the steroidal saponins bethosides B and C was previously assigned as (22R,25R) on the basis of work that employed Horeau's method. Our studies of helosides A and B created doubt about both the original assignment and consequently our conclusion that relied upon it. The absolute configurations of bethosides B and C are revised to (22S,25R) following X-ray crystallographic analysis of their aglycone. Synthesis and full spectral characterization of both the 22R and 22S aglycones is reported to facilitate future stereochemical assignments in this series of saponins.     

Total syntheses of bacillamide C and neobacillamide A; revision of their absolute configurations

The enantiospecific syntheses of both enantiomers of bacillamide C and neobacillamide A are described, along with the measurement of their optical activities, leading to the revision of the proposed absolute configurations of these natural products.     

The first asymmetric total syntheses and determination of absolute configurations of xestodecalactones B and C

The first efficient asymmetric total syntheses of xestodecalactones B and C have been accomplished in 10 steps with an overall yield of 22 and 20.2%, respectively. The key steps involve the utility of Evans oxazolidinone-mediated syn-aldol condensations to establish the C-9 configuration and the macrolide ring formation by intramolecular acylation. The absolute configurations of xestodecalactones B and C have been determined via these syntheses.     

Total syntheses of cladoacetals A and B: confirmation of absolute configurations

The first enantioselective syntheses of cladoacetals A (1a, overall yield: 16%) and B (1b, overall yield: 34%) from crotonaldehyde in nine and seven steps, respectively, have been accomplished. Sharpless asymmetric dihydroxylation, Suzuki coupling, and acid-catalyzed intramolecular acetalization were the key steps in the syntheses. The absolute configuration of natural (+)-cladoacetal A was affirmed to be 1S,3S,4R, whereas that of (-)-cladoacetal B was affirmed to be 1R,3S,4S.     

Enantioselective synthesis and absolute configurations of aculeatins A, B, D, and 6-epi-aculeatin D

The three naturally occurring, bioactive spiroacetals aculeatins A, B, and D, as well as the non-natural 6-epi-aculeatin D have been synthesized for the first time in enantiopure form using an asymmetric allylation as the only chirality source. A further key step was a stereoselective aldol reaction with remote induction. The absolute configurations of the natural products have been established and an erroneous structural assignment has been corrected.     

Relative and absolute configurations of ganefromycin alpha

The full structure of ganefromycin alpha has been determined. The relative configurations were determined from 3JH,H coupling constants and NOE data, while the absolute configurations in moleties A and B were determined separately by difference CD of their acylate derivatives, which showed typical exciton couplets. The configurations of the stereogenic centers in ganefromycin alpha are 8S, 9S, 11R, 12S, 13S, 21S, 22R, 23R, 24R, and 26S.     

Reinvestigation of absolute stereostructure of (-)-rosiridol: structures of monoterpene glycosides, rosiridin, rosiridosides A, B, and C, from Rhodiola sachalinensis

Three new (-)-rosiridol glycosides, rosiridosides A, B, and C, were isolated from the roots of Rhodiola sachalinensis together with rosiridin [(-)-rosiridol 1-O-beta-D-glucopyranoside]. In the course of the structure elucidation of those new glycosides, the absolute configuration of the 4-position in (-)-rosiridol was reinvestigated. On the basis of the application of the modified Mosher's method for (-)- and (+)-rosiridol derivatives, the absolute configuration of the 4-position in (-)-rosiridol should be revised to be S orientation from the recently assigned R form, so that the absolute stereostructures of rosiridosides A, B, and C and rosiridin were determined.     

Phospholipids chiral at phosphorus. synthesis,absolute configurations and applications

Abstract

The synthesis of P-chiral phospholipids is described and their application in stereochemical studies is discussed.     

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 conversion of methylenomycin A to natural botryodiplodin and their absolute configurations

Natural (?)-botryodiplodin($\text{1}$) has been synthesized from an antibiotic methylenomycin A ($\text{2}$). The absolute configurations of (?)-botryodiplodin($\text{1}$ and methylenomycin A ($\text{2}$) have also been established as shown in $\text{1}$ and $\text{2}$ respectively.     

Absolute configurations of griseorhodins A and C

The known antibiotic and cytotoxic compounds griseorhodin A (1) and griseorhodin C (2) were produced in solid culture by Streptomyces puniceus AB10, which was isolated from the leaf-cutter ant Acromyrmex rugosus rugosus. Their absolute configurations were unambiguously established as 6S,6aR,7S,8S and 6R,6aR,7S,8R, respectively, using vibrational circular dichroism (VCD) and density functional theory (DFT) calculations.     

Triterpene glycosides of Pulsatilla dahurica structures of glycosides A,B, C,and D

The isolation of four triterpene glycosides from the roots of the dahurian anemonePulsatilla dahurica (Fisch. ex DC) Spreng, is described together with their identification, on the basis of chemical transformations, spectral characteristics, and literature analogies, as hederagenin 3-O--L-arabinoside, hederagenin 3-O-[O--D-glucopyranosyl-(12)--L-arabinopyranoside], hederagenin 3-O--L-arabinopyranoside 28-O-[O--L-rhamnopyranosyl-(14)--D-glucopyranosyl-(16)--D-glucopyranoside], and hederagenin 3-O-[O--D-glucopyranosyl-(14)--L-arabinopyranoside] 28-O-[O--L-rhamnopyranosyl-(14)--D-glucopyranosyl-(16)--D-glucopyranoside].Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, Russian Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 349–356, May–August, 1992.     

The structures of novel antibiotics,saframycin B and C

The structure of saframycin C(3) has been established by an X-ray crystallographic analysis; this result allows the assignment of structure to the closely related saframycin B(2) by ¹³C NMR spectroscopy.     

Stereo structures and absolute configurations of reaction products of dl-1,3-dimethylthymine epoxide with l-amino acid ethyl esters

Each reaction of dl-1,3-dimethylthymine epoxide ( 1 ) with L-amino acid ethyl esters (Pro-OEt, Met-OEt, Phe-OEt, and Trp-OEt) afforded the respective four optically active diastereomers 4–7 , stereo structures of which were definitely elucidated as shown in Chart 1 by an X-ray analysis of 4A and chemical means.     

Diastereomers of N-alpha-phenylethyl-t-butylsulfinamide: absolute configurations and predominant conformations

N-alpha-Phenylethyl-t-butylsulfinamide is a complicated system for determining molecular stereochemistry because of numerous possibilities for assigning the absolute configuration and a predominant conformation. Two diastereomers of N-alpha-phenylethyl-t-butylsulfinamide derived from (-)-(S)-alpha-phenylethyl amine, a (+)-diastereomer and a (-)-diastereomer, have been synthesized and their experimental chiroptical spectroscopic properties have been measured. These properties include vibrational circular dichroism, electronic circular dichroism and optical rotatory dispersion. Using these experimental data, in conjunction with corresponding density functional theoretical predictions, the absolute configuration and predominant conformations of these two diastereomers have been determined. Also, the absolute configuration of (-)-diastereomer has been independently confirmed by determining its structure from X-ray diffraction data.     

Asymmetric total synthesis and revision of absolute configurations of azaphilone derivative felinone A

The first total synthesis of the azaphilone derivative, felinone A, was accomplished. The absolute configuration of natural felinone A was revised to be 3S, 6S, and 7R.