Pergamon 0031-9422(95)00481-5 Phytocheraistry, Vol. 40, No. 5, pp. 1531 1536, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031 9422/95 $9.50 + 0.00 ISOMERIC TRILUTEOLINS FROM BARTRAMIA STRICTA AND BARTRAMIA POMIFORMIS* TASSILO SEEGER, ARIANE VOIGT, HANS GEIGER, HANS DIETMAR ZINSMEISTER, t GERHARD SCHILLING~ and JOSI~-ANTONIO LOPEZ-SAEZ§ Fachrichtung Botanik, Universit/it des Saarlandes, Postfach 15 11 50, 66041 Saarbriicken, Bundesrepublik Deutschland; :~Organisch-Chemisches Institut, Universit/it, Im Neuenheimer Feld, 69120 Heidelberg, Bundesrepublik Deutschland; §Departemento de Biologia Vegetal I, Universidad Complutense, Ciudad Universitaria, 28040 Madrid, Espafia (Received 28 March 1995) Key Word lndex--Bartramia stricta; B. pomiformis; Bartramiaceae; Musci; bartramiatriluteolin; epibartramiatriluteolin; strictatriluteolin; triluteolins; triflavones. Abstract--From Bartramia stricta and B. pomiformis the new triluteolins epibartramiatriluteolin and strictatriluteolin along with the known bartramiatriluteolin were isolated. The structures and relative stereochemistry of these triluteolins have been elucidated spectroscopically. INTRODUCTION As stated in a preceding paper on bi- and tri-flavonoids from Bartramia stricta, this moss contained in addition to the reported flavonoids a mixture that consists, accord- ing to its NMR spectrum, of at least three further tri- flavones [I]. A small amount of a similar mixture had also been obtained earlier from B. pomiformis 1,2]. After many unsuccessful attempts the separation of this mixture has now been achieved by column chromatography on poly- amide and on Sephadex LH-20 at low temperature (see Experimental). In the present paper the elucidation of the structures of the new compounds is described. RESULTS AND DISCUSSION The first compound, which was later named epibar- tramiatriluteolin (lb), was separated from the bulk of the mixture by column chromatography on polyamide. The relative molecular mass of lb is, as required for a triluteolin, 854 amu ([M - 1-1 anion at 853 m/z in the LAMMA mass spectrum). The NMR data are presented in Table 1. The laCNMR spectrum of lb differs only marginally from that of bartramiatriflavone (la), which occurs also in B. pomiformis [3-1. The coupling patterns of the ~H NMR spectra of la and lb are also the same, only the chemical shifts of the proton signals of the two com- pounds differ markedly. A comparison of the spectra of la and lb with a set of C-H correlated NMR spectra of various biluteolins [4,1 indicates clearly that in both cases the three luteolin moieties are connected via the carbon *Publication No. 87 of'Arbeitskreis Chemic und Biologic der Moose'. 1-Author to whom correspondence should be addressed. atoms IB2', IIA8, IIB2' and IIIA8 (Fig. 1). This allows two possibilities of interflavonyl linkages: Either IB2' ~IIA8 and IIB2' ~ IIIA8 or IB2'-* IIB2' and IIA8 ~ IIIA8. The latter possibility can be excluded, be- cause the resonances of the bridgehead carbon atoms of carbon-carbon linked biflavonoids are shifted downfield from their position in the corresponding monomer (naringenin, apigenin, eriodictyol, taxifolin, luteolin or aureusidin) to a different extent, whether the inter- flavonyl linkage is between two A-rings, two B-rings or an A- and a B-ring. As a rule this shift is about 4.5-6.0 ppm if the linkage is between two A-rings and 10.1-11.4 ppm if it is between two B-rings (e.g. see refs [5,1 and I-6,7,1, respectively). If, however, the interflavonyl linkage is between an A- and a B-ring the situation is quite different (e.g. see refs [3, 8-11,1): In this case the signals of the A-ring bridgehead carbon atoms are ca 9-11 ppm downfield of their position with the corres- ponding monomers, and the downfield shift of the B-ring bridgehead carbon signals is only 4--6.5 ppm. This is the case with la as well as lb, which are therefore both linked IB2' ~ 8IIA and IIB2' --* 8IIIA. Thus, the reason for the different chemical shifts exhibited by the 1HNMR spectra of Is and lb must be caused by a different steric arrangement of the three luteolin moieties with the two compounds. It is known that the rotation round a carbon-carbon interflavonyl bond between a 2' and an 8 position of flavonoids is sterically hindered. Bi- flavonoids having such interflavonyl linkages show atrop- isomerism 1"12]. With triflavonoids having two such link- ages the existence of two diastereomers is to be expected. Figure 2 shows stereo-drawings of the two possible dias- tereomers; they reveal at a glance which formula belongs to which 1HNMR spectrum: Formula la, which has its 1531