Among sesquiterpenes, the most common in Nature and the most intensively studied from all-sided stereochemical aspects are the monocyclic germacranes, of which the bicyclic sesquiterpenes eudesmanes, guaianes, carotanes, and others are considered, to be biogenetic derivatives [1, 2].The germacrane skeleton of these natural compounds is based on the carbon skeleton of cyclodecane with two endocyclic double bonds in the 1(10) and 4(5) positions and methyl groups at C4 and C10 and an isopropyl group at C7, in accordance with the isoprene rule. However, examples are found in which one of the double bonds in the germacranolides is shifted into the 9 = 10 position [3], has been replaced by an epoxide group [4], or is absent [5]. Depending on the cis-or transconfigurations of the endocyclic double bonds (or their substituting epoxide groups) in the 1(10) and 4(5) positions of the cyclodecadiene system, they are classified as representatives of four possible geometric isomers [1, 6]:

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A sesquiterpene lactone of the germacrane series, mucrochin, has been isolated from the epigeal part of Tanacetopsis mucronata, and its structure has been studied by IR and mass spectral methods and PMR spectroscopy. It structure has been determined unambiguously by x-ray structural analysis as 5,6-dihydroxy5c~, 6f3, 7~, 813 (H)-germacra-l (lO), 4(15), 1 (13)-trien-8,12-olide. A boat-chair conformation with a configuration of the 1D 14 15D5 type has been established.Continuing an investigation [1][2][3][4][5] of the plant Tanacetopsis mucronata, we have isolated a sesquiterpene lactone of the germacrane type with mp 181-183~ composition C15H2004, which has been called mucrochin. Its IR spectrum contained absorption bands at (cm -1) 3455 (-OH group), 1735 (C=O of a -y-lactone), 1670 (double bond conjugated with a ~,-lactone carbonyl), and 1658 (isolated C=C bond). In the mass spectrum we observed the peak of the molecular ion with m/z 264 (M +) and peaks of ions with m/z 246 (M + --H20) and 228 (M + --2H20) due to ejection of one and two molecules of water, and also fragments characteristic for breakdown of germacranolides under electron impact (see Experimental section).In .the PMR spectrum, two doublets, each with a 3j value of 3 Hz, appeared at 6.63 and 5.56 ppm. On the addition of very small amounts of trifluoroacetic acid they shifted in the downfield direction, and this showed that they belonged to the protons of two secondary hydroxy groups. The PMR spectrum also contained the signals of the protons of a methyl group at a double bond, of exocyclic methylenes, of protons geminal to a hydroxy group, of a proton on a double bond of the main ring, and of a lactone proton (Table 1). These facts make it possible to assume that mucrochin is a germacranolide. The presence of the resonance lines of two protons at 3.55 and 4.4-4.6 ppm showed the secondary nature of the hydroxy groups. Double-resonance experiments confirmed that they were located vicinally.Signals of the protons of an exomethylene group of a ~,-lactone ring appeared in the form of doublets at 6.46 and 5.77 ppm with 4J7,13 = 3.5, 4J7,13, = 3.0 Hz, which showed a trans-linkage of the "r-lactone ring of type S [6][7][8][9].

UDC 547.992:547.972 We have previously established that the main secondary metabolites of the epigeal part of Tanacetopsis mucronata are the sesquiterpene lactones deacetyllaurenobiolide, balchanolide, isobalchanolide, tanachin, tamirin, tavulin, mycoguanolide, mucrin, mucrolide, mucronin, and mucrochin, and the sesquiterpene alcohol mucrolidin [1, 21. However, TLC analysis of the mother solutions showed the presence of a series of minor components that had not been isolated. By rechromatographing the resin from the mother solutions of the main components we have now isolated four sesquiterpenoids (1 --C15H2204, M + 226, mp 240~ (acetone---hexane); 2 --C30H4207, M + 514, mp 215--217~ 3 --CI5H2204, M + 266, mp 146---148~ (acetone--hexane); and 4 --CIsH2aO 3, M + 256, mp 139--140~ (acetone--hexane)) and two flavonoids (5 --Ci7 I-t14 O 7, M + 330, mp 240~ (acetone hexane); and 6 --CisHt60 a, M + 360, mp 103~ (acetone--hexane).IR spectrum of (1) (KBr, v, cm -I): 3378 (OH groups), 2788 (C H bond of an aldehyde group, 1679 (C=O group of an aldehyde), 1647 (C=C bond).The mass spectrum of (1) revealed the peak of the molecular ion with m/z 266 (M +, C 15H2204, 1%), the peaks of ions with m/z 265 (1.72%), 264 (3.72%), 248 (3.5%), 246 (15%), 230 (6%), 228 (3.93%), 217 (9.5%), 199 (8%), 184-(9.3%), 182 (9.3%), 181 (2.4%), 107 (100%), 29 (32%), 28 (61%), and also other fragments characteristic for the breakdown of eudesmanolides under electron impact.In the PMR spectrum of (1) (Py-d 5) we observed characteristic signals of the protons of three OH groups (5.06, 6.35, 6.46 ppm), the protons of three gem-hydroxy groups (3.74, 4.34, and 4.27 ppm), the protons of an exoeyclic methylene group (6.30 and 6.34 ppm) and of an exomethylene group in a six-membered ring (5.17 and 5.18 ppm), and the signals of the protons of aliphatic methylenes ( 1.77--2.9 ppm), and also a signal of the protons of an angular methyl ( 1.09 ppm).The 13C NMR spectrum (Py-ds) showed signals of the following carbon atoms (ppm): C-1 (77.92), C-2 (32.42), C-3 (35.40), C-4 (144.9), C-5 (57.72), C-6 (67.43), C-7 (55.66), C-8 (77.62), C-9 (41.35), C-10 (43.0), C-I 1 (139.9), C-12 (193.2), C-13 (118.93), C-14 (14.45), C-15 (109.44). On the basis of the spectral characteristics and also of a comparison of them with those of the known lactones (7) [3] and (8) [4] we have proposed structure (1) for the first compound, and we have called it mucrotan.The study of the structures of the other compounds isolated is continuing.

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