Macrolide antibiotics—VII The structure of neomethymycin

Degradation experiments are described which establish rigorously structure (II) for neomethymycin (C₂₅H₄₃NO₇). This antibiotic belongs, therefore, to the macrolide group and differs from methymycin (I) only in the location of one hydroxyl group, which results in marked changes in chemical behavior. The two antibiotics appear to have the same absolute configuration at the relevant asymmetric centers as inferred by the isolation of a common degradation product and the general similarity of certain rotatory dispersion curves. The position of the hydroxyl group at C-12 in neomethymycin is noteworthy from a biogenetic standpoint.     

Stereochemical studies—VIII Unequivocal determination of the absolute configuration in biaryl systems

According to the reaction sequences shown in Figs 1-5, the absolute configuration of optically active biaryl derivatives such as biphenyl, binaphthyl, bianthryl and bianthroaquinonyl have been clearly established, based on the standard compound (R)-(+)-I, in the binaphthyl system, whose absolute configuration was unequivocally determined by the anomalous X-ray diffraction method.     

The absolute configuration of the glutarimide antibiotics streptimiodone and 9-methylstreptimidone.

Chemical and spectroscopic studies have established the absolute configuration of the glutarimide antibiotics streptimidone and 9-methylstreptimidone, which can now be represented as the (2R,5S,6E)-structures 14 and 15 , respectively.     

Terpenoids—II The chemical conversion of enmein into (−)-Kaurane—the absolute configuration of enmein

The acyloin condensation of the lactone ester (III) which was derived from enmein, a diterpenoid bitter principle from Isodon trichocarpus Kudo, afforded several products, the main compound of which was shown to have structure XLII. The latter was converted into (−)-kaurane (LII) through a series of reactions. On the basis of the result, the absolute configuration II of enmein was positively established by a chemical evidence.     

Olivomycin and related antibiotics XXVI. The absolute configurations of olivin and of chromomycinone

Summary The stereochemical correlation of olivin with chromomycinone and the directed degradation of the first of them to di-O-methyl-D-tartaric acid (XXI) has been effected. As a result, it has been shown that olivin and chromomycinone both have the absolute configuration 2S,3R,1S,3S,4R and possess the respective structures (Ia) and (Ib).For Communication XXV, see [1], and for a preliminary communication see [2].M. M. Shemyakin Institute of the Chemistry of Natural Compounds, Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 526–534, July–August, 1972.     

The structure,absolute configuration and biosynthesis of nortiliacorinine a

The incorporation of (±)-norcoclaurine, (±)-coclaurine, (±)-N-methylcoclaurine and dehydro-N-methylcoclaurine into nortiliacorinine A in Tiliacora racemosa colebr has been studied and specific utilisation of the (±)-coclaurine demonstrated. The evidence supports oxidative dimerization of two coclaurine units to give nortiliacorinine A. Experiments with (±)-N-methylcoclaurine and (±)-[1-³H, N-¹⁴CH₃]N-methylcoclaurine established that only one N-methylcoclaurine unit is specifically utilised to constitute that “half” of the base which had phenolic OH group in the benzylic portion and further demonstrated that the H atom at the asymmetric centre in the 1-benzylisoquinoline precursor is retained in the bioconversion into nortiliacorinine A. Double labelling experiment with (±)-[1-³H, 6,0-¹⁴CH₃]N-methylcoclaurine showed that O-Me function of the precursor is lost in the bioconversion into nortiliacorinine A. Parallel feedings of (+)-(S)- and (-)-(R)-N-methyl-coclaurines and (-)-(S)-, and ( + )-(R)-coclaurines revealed that the stereo-specificity is maintained in the biosynthesis of nortiliacorinine A from 1-benzylisoquinoline precursors and established ‘S,S’-configuration at the two asymmetric centres in nortiliacorinine A.     

The structure and absolute configuration of heterophylloidine

The structure and absolute configuration of heterophylloidine, a new C₂₀-diterpenoid alkaloid isolated from $\text{Aconitum heterophylloides}$ Stapf, have been determined with the aid of ¹³C NMR spectral data and single-crystall X-ray analysis of the product obtained by treatment of heterophylloidine with aqueous hydrobromic acid.     

The absolute configuration of berberastine and thalidastine

Optical resolution of (±)-tetrahydrojatrorrhizine using (-)-O,O-di-$\text{p}$-toluoyl-$\text{d}$-tartaric acid gave rise to (+)-tetrahydrojatrorrhizine ($\text{6}$ of high optical purity and of known absolute configuration. Oxidation of this enantiomer with lead tetraacetate, followed by acid hydrolysis, furnished alcohols $\text{10}$ and $\text{11}$ in a 2:1 ratio, whose relative stereochemistry was established from their nmr spectra. Iodine oxidation of the major alcohol $\text{10}$ led to protoberberinium salt $\text{14}$ which was found to be dextrorotatory. Since berberastine ($\text{1}$) and thalidastine ($\text{2}$) are also dextrorotatory, they must possess the same absolute configuration as $\text{14}$.     

Stereoselective synthesis and absolute configuration of epoxyketones in chlamydocin and related cyclic tetrapeptides

The epoxyketone group in the amino acid, 2S-amino-8-oxo-9,10-epoxydecanoic acid (Aoe) has been synthesized by chiral epoxidation of the corresponding allylic alcohol cyclic tetrapeptide precursor to form chlamydocin and epichlamydocin. These compounds have been used as standards to assign by circular dichroism spectroscopy the Aoe epoxyketone configurations in HC-toxin and WF-3161.     

The absolute configuration of 1‐epialexine hemihydrate

The absolute and relative configurations of 1‐epialexine are established by X‐ray crystallographic analysis, giving (1S,2R,3R,7S,7aS)‐1,2,7‐trihydroxy‐3‐(hydroxymethyl)pyrrolizidine. The compound crystallizes as the hemihydrate C₈H₁₅NO₄·0.5H₂O, with hydrogen bonds holding the water molecule in a hydrophilic pocket between epialexine bilayers. In addition, a comparison was made between results obtained from examination of the Bijvoet pairs from data sets collected using molybdenum and copper radiation.     

Botrylactone: new interest in an old molecule—review of its absolute configuration and related compounds

The absolute configuration of botrylactone, a unique compound with an interesting polyketide lactone skeleton with two oxirane bridges previously isolated from Botrytis cinerea and described as a powerful antibiotic, has been reviewed on the basis of sign of the optical rotation, NOE experiments and NMR method. The isolation of 7-deoxybotrylactone and 5-hydroxy-7-(4-hydroxydec-2(3)-enoyl) botrylactone enables us to characterize an intriguing new family of compounds with this interesting polyketide skeleton. A common biosynthetic origin with botcinin derivatives is proposed.     

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.