Control Mechanism for cis Double‐Bond Formation by Polyunsaturated Fatty‐Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final‐product profiles are still obscure. In this study, the FabA‐type dehydratase domain (DH_FabA) in the C‐subunit and the polyketide synthase‐type dehydratase domain (DH_PKS) in the B‐subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C₄‐ to C₈‐acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DH_PKS and DH_FabA, depending on the carbon‐chain length, to introduce either saturation or cis double bonds to growing acyl chains.     

A new level at 192.5 keV in Ge

In the experiments on ⁷⁴Ge(d, pγ)⁷⁵Ge, a 52.5±0.1 keV γ-ray was found in ⁷⁵Ge with a half-life of 216±5 ns. From the analysis of the γ-ray spectra the conversion coefficient of the 52.5 keV γ-ray was determined. Then, a new level of is confirmed to exist at 192.5 keV. The reduced transition probabilities of the 52.5 keV transition are deduced to be (6.9^+5.6 _−2.1) × 10⁻⁵ for B(M1) and 31⁺³ ₋₂ for B(E2) in Weisskopf units.     

A rotational band in82Zr

The neutron deficient nucleus⁸²Zr has been studied through the reaction⁵⁸Ni(²⁸Si, 2p 2n)⁸²Zr with a calculated cross section of 0.3% of the total fusion cross section atE(²⁸Si)=128 MeV. Gamma rays from excited states of⁸²Zr were measured and identified using the NORDBALL escape-suppression array at the Niels Bohr Institute. Reaction channel selection was performed by use of neutron and charged particle detector arrays in conjunction with the germanium detectors. A rotational band in⁸²Zr has been identified with spins up to 20 ? by analysis of reaction channel selectedγ-γ coincidence matrices. Band crossings were identified at frequencies 0.57 and 0.69 MeV.     

A new general method for synthesis of ketene dithioacetal

Dithioacetals ($\text{1}$) were treated with n-butyllithium and 2,2′-dipyridyl disulfide to give ketene dithioacetals ($\text{3}$) in high yields, which constituted a new efficient synthetic method for the latter compounds.     

Enantioselective microbial hydroxylation of bicyclo(2.2.1)heptane carbon skeleton

Bicyclo(2.2.1)heptane-7-carboxylic acid ($\text{9}$) and methyl bicyclo(2.2.1)hept-2-ene-7-$\text{syn}$-carboxylate ($\text{5}$) were microbiologically hydroxylated to give (1$\text{R}$)-2-hydroxy derivatives.     

Anti-androgenic triterpenoids from the Brazilian medicinal plant, Cordia multispicata

Compounds 1-6 were isolated from the AcOEt soluble fraction of leaves of the Brazilian medicinal plant, Cordia multispicata, and their structures were elucidated to be 3beta,25-epoxy-21beta-acetoxy-3alpha,22beta-dihydroxyurs-12-en-28-al (1), 3beta,25-epoxy-28-acetoxy-3alpha,21beta,22beta-trihydroxyurs-12-ene (2), 21beta-acetoxy-22beta-hydroxy-3-oxours-12-en-28-al (3), 28-acetoxy-6beta, 21beta,22beta-trihydroxy-3-oxours-12-ene (4), 21beta,22beta-dihydroxy-3-oxours-1 2-en-28-al (5) and 3beta,21beta,22beta-trihydroxyurs-I2-en-28-al (6), respectively, by means of spectral data, especially two dimensional NMR techniques. Triterpenes having the hemiketal structure at the A-ring, an acyloxy group at C-22 and/or ketone at C-3 showed potent anti-androgenic activity.     

Cholestane glycosides from Solanum abutiloides. III

Four new cholestane glycosides, named abutilosides D (1), E (2), F (3) and G (4), were isolated from the fresh roots of Solanum abutiloides. By chemical and spectroscopic evidence, their structures were elucidated as 26-O-beta-D-glucopyranosyl 3beta,16alpha,26-trihydroxy-5alpha-cholestan-22-one 3-O-beta-D-xylopyranosyl-(1-->2)-alpha-L-rhamnopyranosyl-(1-->4)-beta-D- glucopyranoside and its desxylosyl compound (1 and 3, respectively), 26-O-beta-D-glucopyranosyl 3beta,16alpha,26-trihydroxycholest-5-en-22-one 3-O-beta-D-xylopyranosyl-(1-->2)-alpha-L-rhamnopyranosyl-(1-->4)-beta-D- glucopyranoside and its desxylosyl compound (2 and 4, respectively). These compounds were regarded as precursors of a dormantinone type compound on a hypothetical pathway of steroid biogenesis.