Dimunito/Dwarf1 (DWF1) is an oxidoreductase enzyme that is responsible for the conversion of C 28 -and C 29 -⌬ 24(28) -olefinic sterols to 24-methyl-and 24-ethylcholesterols. Generally, the reaction proceeds in two steps via the ⌬ 24(25) intermediate. In this study, we characterized the ArDWF1 gene from an expression sequence tag library of Ajuga reptans var. atropurpurea hairy roots. The gene was functionally expressed in the yeast T21 strain. The in vivo and in vitro study of the transformed yeast indicated that ArDWF1 catalyzes the conversion of 24-methylenecholesterol to campesterol. A labeling study followed by GC-MS analysis suggested that the reaction proceeded with retention of the C-25 hydrogen. The 25-H retention was established by the incubation of the enzyme with (23,23,25-2 H 3 ,28-13 C)-24-methylenecholesterol, followed by 13 C NMR analysis of the resulting campesterol. Thus, it has been concluded that ArDWF1 directly reduces 24-methylenecholesterol to produce campesterol without passing through a ⌬ 24(25) intermediate. This is the first characterization of such a unique DWF1 enzyme. For comparison purposes, Oryza sativa DWF1 (OsDWF1) was similarly expressed in yeast. An in vivo assay of OsDWF1 supported the generally accepted two-step mechanism because the C-25 hydrogen of 24-methylenecholesterol was eliminated during its conversion to 24-methylcholesterol. As expected, the 24-methylcholesterol produced by OsDWF1 was a mixture of campesterol and dihydrobrassicasterol. Furthermore, the 24-methylcholesterol contained in the Ajuga hairy roots was determined to be solely campesterol through its analysis using chiral GC-MS. Therefore, ArDWF1 has another unique property in that only campesterol is formed by the direct reduction catalyzed by the enzyme.In vertebrates, cholesterol is the major sterol, whereas, in higher plants, commonly occurring sterols are C 29 sterols, sitosterol (1) and stigmasterol, and a C 28 sterol, campesterol (2). Campesterol is frequently accompanied by dihydrobrassicasterol (3) (1, 2). Latter steps in phytosterol biosynthesis have received considerable attention because of their intriguing chemistry, biochemistry, and biology. Recent studies through genetic mutations have uncovered an essential role of these phytosterols at the cellular level in hormone signaling, organized divisions, and embryo patterning (3).It is generally regarded that these typical plant sterols are biosynthesized from precursor ⌬ 24(28) -olefinic sterols, i.e. isofucosterol (4) and 24-methylenecholesterol (5), in two steps: a double-bond isomerization from ⌬ 24(28) to ⌬ 24(25) (leading to 24-ethyldesmosterol (6) and 24-methyldesmosterol (7)) and a reduction of the ⌬ 24(25) intermediates to the saturated C 29 and C 28 sterols (1 and 2/3). Interestingly, the reduction of 24-ethyldesmosterol affords only sitosterol, whereas the reduction of 24-methyldesmosterol yields a C-24 epimeric mixture of campesterol and dihydrobrassicasterol (1, 2). The two-step mechanism has been proposed mainly on the basis of the m...

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The first total syntheses of acetogenin 3 and its 4S,8R-isomer are described. The key step involves intermolecular metathesis of an r,βunsaturated ketone carrying a tetrahydropyranyl lactone with a tetrahydrofuran derivative. Compound 3 has spectroscopic and physical data consistent with those of natural montanacin D, suggesting that the absolute configuration of the natural product is as shown in 3.The Annonaceous acetogenins from the Annonaceae plants comprise a class of almost 400 natural products that exhibit a remarkably broad spectrum of biological properties such as anticancer, antiinfective, immunosuppressive, pesticidal, and antifeedant activities. 1 Structurally, most of these compounds belong to several classic types with an unsubstituted tetrahydrofuran (THF) ring: the mono-THF, the adjacent bis-THF, and the nonadjacent bis-THF acetogenins. Recently, several nonclassical acetogenins have been discovered bearing a tetrahydropyran (THP) ring. 2 In 1999, Qin and Cheng et al. isolated montanacin D from the ethanolic extract of the leaves of Annona montana. 3 The structure was elucidated by chemical and spectral means to be 1 possessing a 4,8-cis THP ring along with a 16,19-trans THF ring (Figure 1). 4 However, the absolute configuration of the THP ring part was not determined. Unlike the other approximately 420 acetogenins, the presence of the THP ring adjacent to the butenolide moiety in 1 provides a confor-

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