Draft genome of Omphalotus olearius provides a predictive framework for sesquiterpenoid natural product biosynthesis in Basidiomycota

The secondary metabolome of Basidiomycota represents a largely uncharacterized source of pharmaceutically relevant natural products. Terpenoids are the primary class of bioactive compounds isolated from mushrooms. The Jack O'Lantern mushroom Omphalotus olearius was identified 50 years ago as a prolific producer of anticancer illudin sesquiterpenoids; however, to date there have been exceptionally few studies into the biosynthesis of these important compounds. Here, we report the draft genome sequence of O. olearius, which reveals a diverse network of sesquiterpene synthases and two metabolic gene clusters associated with illudin biosynthesis. Characterization of the sesquiterpene synthases enabled a comprehensive survey of all currently available Basidiomycota genomes, thereby creating a predictive resource for terpenoid natural product biosynthesis in these organisms. Our results will facilitate discovery and biosynthetic production of unique pharmaceutically relevant bioactive compounds from Basidiomycota.     

Diels-Alder adducts of 4-chloro-1,6-dihydrophosphinine derivatives: A new precursor of 2-phosphapropene

The 4-chloro-1,6-dihydrophosphinine derivatives, prepared as a mixture of 3- and 5-methyl isomers from the thermolysis of dichlorocarbene adducts with 1-R-3-methylphospholene oxide (R  Me, MeO, EtO, n-PrO, i-PrO), participate in Diels-Alder reactions with dimethyl acetylenedicarboxylate and N-phenylmaleimide. The former reactant is of special value since the 2-phosphabicyclo[2.2.2]octa-5,7-diene framework is thermally labile and undergoes retrocycloaddition by a different path, eliminating the C P bridging unit as a low-coordinate species. Thus, in the case of R  Me, the initial phosphine oxides (a mixture of isomers) have been reduced to the phosphines and these undergo straightforward fragmentations on heating at 50°C to produce 2-phosphapropene. The reactions of this transient species with water and alcohols have been investigated. Unlike the case of stabilized phosphaalkenes, hydration occurs smoothly without catalysis to produce Me₂P(O)H; addition of alcohols gives phosphinites, Me₂POR. The structure of the Diels-Alder adducts was confirmed by ³¹P, ¹H, and ¹³C NMR spectroscopy. Each of the isomeric 1,6-dihydrophosphinine oxides gives two diastereomeric adducts; partial separation of some of the resulting four-component mixtures was achieved with silica gel chromatography.     

Diketones from ozonolysis of fused 3-phospholene oxides: Cyclizations to 3-phosphorinone and to 1,4-dihydro-1,4-azaphosphinine derivatives

1-R-3-Methyl-2,4,5,6,7,7a-hexahydro-1(H)-phosphindole 1-oxide and 1-R-3-methyl-6-methoxy-2,8,9,9a-tetrahydro-1(H)-benzo[e]phosphindole 1-oxide (R = Me or Ph) were prepared and ozonized at −78°C to give diketones in good yield. The intramolecular aldol condensation was performed on certain of these ketones to give multicyclic 3-phosphorinone derivatives. In some cases, double-bond rearrangement into the ring-fusion position was encountered. The 1-phenyl derivative in the benzophosphindole series could not be cyclized due to ready displacement of the P fragment from the tetralone system. The diketones reacted with ammonium acetate to give multicyclic derivatives of the 1,4-dihydro-1,4-azaphosphinine ring system. 1,2,3,4,5,6,7,8-Octahydro-3-oxo-1-phenylphosphinoline 1-oxide was used to demonstrate the value of the bicyclic 3-phosphorinones as precursors of 1-phosphadecalone derivatives. The carbonyl group was protected as the ethylene ketal and the double bond (as well as the benzene ring) was hydrogenated with ease. Hydrolysis gave the 1-phospha-3-decalone derivative. Reduction of the same 3-phosphorinone with NaBH₄ gave a mixture of diastereomeric alcohols.     

Comparison of steric effects on 31P chemical shifts in some 7-norbornyl, 7-norbornenyl and cyclohexyl phosphorus compounds

Phosphorus-31 NMR spectra were obtained on both syn and anti isomers of norbornenes with the 7-position bearing Cl₂P-, Me₂P-, Me₂(S)P- and Me₃P as substituents. Norbornanes with 7-Cl₂P- and 7-Me₂P- were also studied. Just as is true for ¹³C shifts for 7-Me in these bicyclo[2.2.1]heptane derivatives, the ³¹P shifts all fall noticeably upfield of published values for comparable cyclohexane derivatives. Consistent also with the ¹³C effect, a slight shielding of ³¹P in Me₂P- (1.1 ppm) was noted when this group was syn to the double bond of the norbornene system, relative to the value for the anti compound, suggesting the sensitivity of ³¹P to a diamagnetic effect from the double bond. However, the more space-demanding Cl₂P group when moved from the crowded anti to the less crowded syn position experienced a strong deshielding effect, as did the Me₂(S)P- and Me₃P- groups. The opposite is seen when these same groups are moved from the crowded axial to the less crowded equatorial position of cyclohexane, and a new structural influence appears to be operating in this system. A recent proposal that steric compression causes bond angles about phosphorus to increase and that this is the cause of the γ-shielding effect is not supported by published NMR and X-ray structural data for cis- and trans-1-methyl-4-tert-butyl-4-phosphorinanol. Bond angles about phosphorus are virtually identical in these isomers, yet ³¹P shifts differ by 6.9 ppm.     

Study of stripping to levels of 21Ne

Angular distributions of the cross section and vector analyzing power have been measured for 8 levels in ²¹Ne using the ²⁰Ne($\text{d}$, p)²¹Ne reaction. New spin assignments are made to the 4.52 MeV level ($\text{J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{+}}$) and the 5.69 MeV level ($\text{J}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}^{\mathrm{?}}$). Our results support a $\text{J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{+}}$ assignment to the 5.33 MeV level and disagree with the $\text{J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{+}}$ assignment to the 3.73 MeV level.     

The molecular and crystal structure of endo-2-methyl-7-hydroxy-7-oxo-N-phenyl-7-phosphabicyclo-[2.2.1] hept-2-ene-5,6-dicarboximide

The structure of the title compound1 has been determined by X-ray crystallography analysis. The following crystal data were found: orthorhombic,Pca2_l,a=9.60691),b=16.356(1),c=8.686(1) . Both the phospholane and phospholene rings involved in the 7-phosphabicyclo-[2.2.1] hept-2-ene system have almost regular envelope conformations, and the cyclohexene ring has a significantly deformed boat conformation. The low value of the C–P–C angle, 84.2(2)°, reflects the steric strain around the phosphorus bridge and may be responsible for the reactivity of esters and amides derived from1 in the O-insertion reaction with m-chloro-perbenzoic acid. The dihedral angle between the plane of the benzene and succinimide rings is 82.4(2)°.     

33S NMR spectra of sulfonium salts: calculated and experimental

33S NMR chemical shifts were calculated by the scaled DFT and EMPI approaches for the fluoride, chloride and bromide of trimethylsulfonium ion (1) and S-methyltetrahydrothiophenium ion (2), in addition to the free cations. Experimental values were obtained for the iodides of 1 (delta +48, CS2 = 0 ppm) and 2 (delta +95), and were found to agree with the calculated values well within the standard deviation of 35 ppm (3.5% of the shielding range) established in earlier work for a great variety of sulfur compounds. An earlier literature value of delta +750 for the iodide of 2 is therefore to be replaced. Calculations provide a shift of delta +68 for S-methylthianium ion with equatorial methyl, indicating that the reported value of delta +670 for the iodide is also incorrect.     

Nature of bonding in the sulfuryl group

The SO sulfuryl bond in a number of representative sulfoxides and sulfones has been studied at the B3LYP/6-311+G(d,p) level in the atoms-in-molecules (AIM) approach involving the AIM delocalization index and the Cioslowski-Mixon localized orbitals and associated covalent bond order. The sulfur-oxygen covalent bond is strongly polarized toward oxygen and the oxygen lone pairs provide significant backbonding to create short and strong SO bonds, similar in nature to those found in the analogous phosphoryl (PO) bond. Although the sulfoxides in general have larger delocalization indices than the sulfones, there is no correlation between these quantities and the bond dissociation energies.