Karl H. Overton

Tetranortriterpenoids—VIII : The constitution and stereochemistry of nimbin☆

Abstract The recorded evidence 3,4 bearing on the constitution of nimbin has been evaluated. By using spectroscopic and additional chemical evidence and making certain biogenetic assumptions, the constitution and stereochemistry (I) are deduced for nimbin. Pyronimbic acid 3 is formulated as XI. The dilactone XVII holds an important place in the structural argument.

Formation of three new flavones by differentiating callus cultures of andrographis paniculata

Abstract Differentiating tissue cultures of Andrographis paniculata produce three new flavones, 5-hydroxy-7,8,2′-trimethoxy-, 5,2′-dihydroxy-7,8-dimethoxy- and 5-hydroxy-7,8-dimethoxy-flavones. Flavones are not synthesized by the de-differentiated callus. Closely related flavones have been isolated from intact plants of Andrographis species.

Tetranortriterpenoids—VII : [Bicyclononanolides—V] the constitution and stereochemistry of swietenolide☆☆☆

Abstract The constitution and stereochemistry of swietenolide (I) are deduced from its spectroscopic and chemical properties and confirmed b cleavage of the β-diketone VIIa or VIIIa (R  OH) to the mono- and di-carboxylic acids corresponding to XIII and XIV. The absolute configuration of swietenolide as in I follows from the CD of XIII.4

Asymmetric syntheses of the naturally occurring β-amino acids, β-lysine, β-leucine and β-phenyl-β-alanine via nitrone cycloaddition

A general asymmetric synthesis of β-amino acids is based on the dipolar cycloaddition of nitrones 7(R* chiral) with vinyl acetate 8a, ketene acetals 8b or α-chloroacrylonitrile 8c. The cycloadducts 9 are converted either directly (9b) or via the isoxazolidinones 10(9a, 9c) into the free β-amino acids 11. Diastereoselectivity at C-3 in the adducts 9 ranges between 2:1 and 11 :1. The natural β-amino acids, β-lysine, β-leucine and β-phenyl-β-alanine, have been prepared in this way.

Interconversion of trans, trans and cis, trans farnesol by enzymes from Andrographis

Abstract When trans , trans -farnesol [4,8,12- 14 C 3 ,1- 3 H 2 ] is isomerized to cis , trans -farnesol by soluble enzymes from Andrographis paniculata tissue cultures, 50% of the tritium label is lost. The same loss is observed when isomerization occurs in the opposite direction. This is in accordance with the proposed mechanism for isomerization via aldehydes.

Tetranortriterpenoids—IV : [Bicyclononanolides II] The constitution and stereochemistry of mexicanolide

Abstract The constitution of mexicanolide (I) is deduced from two key reactions. Under very mild basic conditions mexicanolide fragments to form the diketone IVa or Va. This in turn is cleaved by periodate to the triacid X (R = H) and the monoacid XI (R = H) see Part VII. These cleavage products are uniquely defined by their spectroscopic attributes. The absolute configuration of mexicanolide follows from the CD of the diene lactones IVa or Va and XI.

The diterpenes from the leaves of Cryptomeria japonica

Abstract Cryptomeria japonica trees can be sub-divided into four chemically distinct varieties on the basis of the diterpene hydrocarbon content of their leaves. Seven other species from the Taxodiaceae have been analysed for diterpenes.

The alternative occurrence of (−)-kaurene or (+)-phyllocladene in the leaves of cryptomeria japonica D. Don

Abstract Foliage from Cryptomeria japonica D. Don was analysed for diterpenoid hydrocarbons. Samples grown from some seed sources furnished (−)-kaurene as the sole product of this type, whilst those from other sources yielded only (+)-phyllocladene. These observations were found to be seasonally independent and it is concluded that C. japonica exists in two chemically distinct forms.

Cyclisation of farnesyl pyrophosphate to γ-bisabolene in tissue cultures of Andrographis paniculata

Tissue Cultures of Andrographis paniculate transform trans,trans-[1-3H2; 12,13-14C2]farnesy pyrophosphate, and (3R,5R)- and (3R,5S)-(5-3H)-mevalonolactones into Z-γ-bisabolene without tritium loss; the absolute configuration of paniculide B (7a) has been determined by an X-ray crystal structure determination of its bis-p-bropmobenzoate.

Tetranortriterpenoids—III : 6-Hydroxy- and 6-acetoxy- methyl angolensate from the heartwood of Khaya grandifoliola☆

Abstract Two new tetranortriterpenoids from the heartwood of Khaya grandifoliola are shown to be methyl 6-hydroxy- and methyl 6-acetoxy- angolensate, by analysis of their NMR spectra, using single and double irradiation.