The stereochemistry1 of terpenoid coumarins

Summary A transition has been effected between three series of terpenoid coumarins. A method has been proposed for establishing the type of linkage of the rings of coumarins with the bicyclofarnesyl residue according to the sign of the rotation of the compound concerned.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 707–712, November–December, 1978. Original article submitted April 26, 1978.     

The stereochemistry of ketoreduction

In this issue of Chemistry & Biology, Leadlay and coworkers report overproduction of a number of ketoreductase domains from modular polyketide synthases. These discrete enzymes allow the stereochemistry of polyketide ketoreduction to be studied in isolation.     

The stereochemistry of heterocycles

Fifteen previously unreported 2-alkyl- and 5-alkyl-2, 2-dimethyl-1, 3-dithianes have been synthesized by the condensation of 2-alkylpropane-1, 3-dithiols with acetaldehyde, isobutylraldehyde, and acetone, and their structures have been confirmed by their IR spectra. The existence of stereoisomers in a number of the thioacetals has been shown by GLC and TLC. Some of the stereoisomeric 2, 5-diakyl-1, 3-dithianes have been separated by fractionation in an efficient column into the individual isomers, the purity of which was confirmed by TLC, GLC, and IR spectroscopy.For part III, see [11].     

The stereochemistry of nevskin

Summary The relative configurations of the substituents in nevskin have been determined from the H¹ NMR spectra in CDCl₃ with additions of Eu(FOD)₃ as paramagnetic shift reagent.Institute of Botany, Academy of Sciences of the Azerbaidzhan SSR, Baku. All-Union Scientific-Research Institute of Medicinal Plants, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 450–452, July–August, 1976.     

The stereochemistry of myxothiazol

The absolute configuration of myxothiazol is established as 4(6-carbamoyl-3S,5-dimethoxy-4R-methylhexa-1E,5E-dienyl)-2′-(1S ,6-dimethylhepta-2E,4E-dienyl)-2,4′-bithiazole by a combination of chemical methods and X-ray analysis     

The stereochemistry of chuangxinmycin

Chuangxinmycin was shown by chemical correlation to have 35, 4R configuration as shown by 1. It is surprising that I has the opposite absolute configuration as indolmycin (7) with the same carbon skeleton. The carboxyl group of norchuangxinmycin (14) and the methyl group of decarboxychuangxinmycin (18) were found to have preferred equatorial conformations with no observable anomeric effect in the former. Thus the bulkier carboxyl group of chuangxinmycin itself must adopt the equatorial position predominantly, if not exclusively, in solution, a situation already found prevailing in the crystalline state by X-ray diffraction.     

The stereochemistry of quassin

The relative configuration of quassin and several of its derivatives has been derived.     

The stereochemistry of allohimachalol

Allohimachalol, an unusual rearranged sesquiterpene from the essential oil of $\text{Cedrus}$$\text{deodara}$ Loud., is shown to have structure 3.     

创新霉素的立体化学研究

由化学方法证明创新霉素的绝对构型为3S,4R,如式1所示. 与已知具有相同骨架的臧生素indolmycin(7)的绝对构型相反, 为生源方面饶有兴趣的问题. 去甲创新霉素(14)的羧基及去羧色新霉素(18)的甲基均以横键为最佳构象, 因此似无顶端(anomeric)效应. 由此可以推断创新霉素在溶液中较大的羧基是模键, 甲基是竖键. 这一点与固态X衍射结果一致.     

1-Oxo-1,3-dithiolanes--synthesis and stereochemistry

1-Oxo-1,3-dithiolane (4) and its cis- and trans-2-methyl (5,6), -4-methyl (7,8) and -5-methyl (9,10) derivatives were prepared by oxidizing the corresponding 1,3-dithiolanes (1-3) with NaIO(4) in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with (1)H and (13)C NMR spectroscopy and molecular modelling. The sulfoxides 4-6 and 8-10 attain two S(1) type envelopes (sometimes slightly distorted) the S=O(ax) envelope greatly dominating. Cis-4-methyl-1-oxo-1,3-dithiolane is a special case exhibiting both two closely related S=O(ax) (30 and 27%) as well as S=O(eq) (21 and 22%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of (1)H-(1)H coupling constants and (1)H and (13)C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data.