The Absolute Configuration of the Fungal Metabolite Verrucarin B. Biosynthetic Consequences. Verrucarins and roridins, 36th communication

HELVETICA CHIMICA ACTA - Vol. 62, Fasc. 8 (1979) - Nr. 273 2699 273. The Absolute Configuration of the Fungal Metabolite Verrucarin B. Biosynthetic Consequences Verrucarins and Roridins, 36th Communication [ 11 by Werner Breitenstein and Christoph Tamm') Institut fur Organische Chemie der Universitat. St. Johanns-Ring 19, CH-4056 Basel and Edward V. Arnold and Jon Clardy') Department of Chemistry, Cornell University, Ithaca, NY 14853, U.S.A. (2. x. 79) Summary The absolute configuration of verrucarin B (2) has been determined by a single crystal X-ray diffraction analysis. This result permits the stereochemistry of the biogenetic transformation of mevalonic acid (12) to verrucarinic acid (7) to be deduced. Introduction. - Verrucarin B (2) [2] belongs to a complex of closely related mould metabolites which have been isolated during the past seventeen years from various strains of Myrothecium verrucaria and Myrothecium roridum [3]. The members of this class of natural products, which includes verrucarin A (1) [4], verrucarin B (2) [2], verrucarin J (3) [ 5 ] , 2'-dehydroverrucarin A (4) [6], roridin A [7], roridin D (16) [8], roridin E [9] and roridin H [lo], exhibit remarkable biological effects such as antibiotic, antifungal and antitumor activity. These metabolites have structures closely related to each other [l 11 and are characterized either as macrocyclic diesters (roridin series) or as triesters (verrucarin series) of the sesquiterpene alcohol verrucarol (5) [ 121 which belongs to the trichothecene group [ 131. In recent years a large number of natural products belonging to the same family have become known. These include satratoxin H [14], a toxic metabolite of Stachybotrys atra, verrucarin K [ 151, vertisporin [ 161, a metabolite of Verticimono- sporium diffractum, as well as isororidin E, epoxyroridin E, epoxyroridin H and diepoxyroridin H [17], which have been isolated from a Cylindrocarpon species. Baccharin, the recently discovered antileukemic principle of Baccharis megapo- tamica, is the first macrocyclic trichothecene derivative obtained from a higher plant [ 181. The close structural relationship of these natural products suggested a common biogenetic pathway. I) Authors to whom correspondence should be addressed. 0018-019X/79/8/2699-07$01.00/0 0 1979 Schweizerische Chemische Gesellschaft 2700 HELVETICA CHIMICA ACTA - Vol. 62, Fasc. 8 (1979) - Nr. 273 1 Verrucarin A 2 Verrucarin 0 3 Verrucarin J 4 2 - Dehydroverrucarin A In 1971 Achini et al. [I91 reported the first results of their biosynthetic studies on the verrucarins and roridins. Base catalyzed hydrolysis was a key reaction, allowing the dissection of the original molecules into the trichothecene moiety and the carboxylic acids which form the macrocyclic esters while avoiding the formation of artifacts 1201. In the case of verrucarin A (1) this cleavage yielded the Scheme I 1 Verrucarin A 5 Verrucarol 6 Z, E-Muconic Acid 7 Verrucarinic Acid 8 Verrucarinolactonc HELVETICA CHIMICA ACTA - Vol. 62, Fasc. 8 (1979) - Nr. 273 2701 sesquiterpene alcohol verrucarol (9, (Z,E)-muconic acid (6), and verrucarinic acid (7) isolated as the lactone 8 (Scheme I). Application of this procedure to a radioactive preparation of verrucarin A (1) which had been enriched by the incorporation of [2-3H2, 2-14C]-mevalonate demonstrated that mevalonic acid (12) serves as a biogenetic precursor of the isomeric verrucarinic acid (7), the cleavage product of verrucarin A [2 11. In addition, during this biogenetic conversion, the pro-R-2-hydrogen atom of mevalonic acid (12) migrates to C(3) of verrucarinic acid (7). On the basis of these observations a potential mechanism was proposed for the transformation of mevalonate (9) into verrucarinate (11) which used 2,3-epoxyanhydromevalonate (10) as an intermediate [2 13. The postulated intermediate 10 is apparently incorporated in verrucarin B (2). However, no reliable information concerning the configuration of 10 as it occurred in verrucarin B was available. Furthermore, several problems related to the stereochemistry of the biosynthetic conversion of mevalonate (9) into verru- carinate (11) remained unsolved. In order to remove this uncertainty the absolute configuration of verrucarin B (2) was determined by X-ray diffraction, thus also establishing the absolute configuration of 2,3-epoxyanhydromevalonate (10). This paper reports the results of these investigations and their implications for the biosynthesis of the verrucarins and roridins. c, I H3 HO , P 3 HO Ao0--- HO doe- - - HO 9 10 11 Rontgen-diffraction of verrucarin B. - The crystal chosen for X-ray analysis was roughly rectangular with dimensions of 0.5 x 0.25 x 0.25 mm. Preliminary X-ray photographs showed that the crystal was monoclinic. Accurate lattice constants, determined by a least-squares fit of fifteen moderate 2 @-values, were a= 10.443 (3), b=8.946 (3), c= 14.361 (3) A and p=98.81 (2)". The systematic extinctions (OkO, absent if k = 2 n + l) , a crystal density of 1.26 g/cm3 and the known chirality were uniquely accommodated by space group P2, with one molecule of composition C27H3209 per asymmetric unit. All independent diffraction maxima with 2 0 - 50" (sin @ / I . - 0.959) were surveyed on a fully automated four- 92 Figure. Stereoscopic projection of verrucarin B (2) T ab le . F ra ct io na l co or di na te s an d le m pe ra tu re fa ct or s fo r V er ru ca ri n B (2 ). St an da rd d ev ia tio ns o f th e le as t si gn if ic an t fig ur es a re g iv en i n pa re nt he se s. 5 H yd ro ge ns a re a ss ig ne d th e sa m e nu m be rs a s th e he av y at om s to w hi ch th ey a re b on de d. E3 A to m X Y c1 c 2 c 3 c 4 c 5 C 6 c 7 C 8 c 9 c 1 0 c1 1 c 1 2 C 13 C I4 C 15 C I6 C 1 7 C 18 C 19 c 2 0 c2 1 c 2 2 C 23 C 24 C 25 C 26 C 27 0 2 8 02 9 0 30 0 3 1 0 32 0 3 3 0. 15 68 (3 ) 0. 19 87 (3 ) 0. 23 59 (3 ) 0. 22 03 (3 ) 0. 07 42 (3 ) 0. 04 51 (3 ) - 0 .0 95 4 (4 ) -0 .1 90 6( 3) - 0. 15 37 (3 ) -0 ,0 17 4 (3 ) 0. 23 69 (3 ) 0. 28 14 (4 ) 0. 31 83 ( 3) 0. 03 81 (3 ) 0. 04 86 (5 ) 0. 13 13 (5 ) 0. 16 62 (5 ) 0. 29 02 (6 ) 0. 40 52 (7 ) 0. 12 99 (1 2) 0. 58 38 (5 ) 0. 63 57 (5 ) 0. 56 42 (4 ) 0. 61 88 (4 ) 0. 55 08 (4 ) 0. 40 76 (3 ) 0. 02 29 (2 ) 0. 36 75 (2 ) 0. 10 25 (3 ) 0. 06 93 (4 ) 0. 46 05 (4 ) - 0. 32 99 (4 ) - 0. 05 5 1 (4 ) 0. 79 00 (1 1) 0. 63 87 (1 1) 0. 54 81 (1 1) 0. 65 60 (1 1) 0. 64 78 (1 1) 0. 76 83 (1 1) 0. 76 48 (1 1) 0. 75 12 (1 1) 0. 70 98 (1 1) 0. 67 45 (1 1) 0. 80 42 (1 1) 0. 94 42 (1 1) 0. 63 33 (1 1) 0. 49 31 (1 1) 0. 78 70 (1 3) 0. 36 63 (1 2) 0. 33 67 (1 2) 0. 18 34 ( 12 ) 0. 17 08 (1 4) 0. 09 85 (1 6) 0. 04 85 (1 4) 0. 15 50 (1 3) 0. 21 33 (1 3) 0. 26 02 (1 2) 0. 3 1 45 ,( 1 2) 0. 36 99 (1 2) 0. 38 13 (1 1) 0. 79 67 (1 0) 0. 85 79 (1 1) 0. 46 26 (1 1) 0. 31 00 (1 3) 0. 26 65 (1 2) 0. 16 73 (1 2) Z B 11 or B B 22 B 33 B 12 B1 3 B 23 0. 00 52 ( 2) 0. 06 33 ( 2) 0. 14 71 (2 ) 0. 16 49 (2 ) 0. 23 55 (2 ) 0. 25 23 (3 ) 0. 16 29 (3 ) 0. 08 38 (2 ) 0. 07 08 (2 ) 0. 09 96 (2 ) 0. 14 51 (3 ) 0. 23 54 (2 ) 0. 19 73 (2 ) 0. 17 32 (4 ) 0. 34 21 (3 ) 0. 43 26 (3 ) 0. 46 72 (3 ) 0. 54 30 (3 ) 0. 52 47 (4 ) 0. 41 40 (6 ) 0. 45 21 ( 3) 0. 36 99 (3 ) 0. 29 21 (3 ) 0. 13 23 (3 ) 0. 01 61 (2 ) 0. 09 80 (2 ) 0. 29 15 (1 5) 0. 31 59 (4 ) 0. 50 18 (2 ) 0. 44 83 (3 ) - 0. 02 73 (2 ) 0. 21 20 (3 ) 0. 1 1 74 (2 ) 0. 00 95 (3 ) 0. 01 07 ( 3) 0. 00 85 (3 ) 0. 00 69 (3 ) 0. 00 73 (3 ) 0. 00 96 (3 ) 0. 01 05 (4 ) 0. 00 80 (3 ) 0. 00 80 ( 3) 0. 00 82 (3 ) 0. 00 76 (3 ) 0. 01 36 (5 ) 0. 00 86 (3 ) 0. 00 83 (3 ) 0. 00 82 (4 ) 0. 01 30 (5 ) 0. 01 74 (6 ) 0. 02 38 (9 ) 0. 02 18 (1 0) 0. 04 93 (2 3) 0. 01 80 (7 ) 0. 01 43 (5 ) 0. 01 1 4 ( 4) 0. 01 00 (4 ) 0. 01 18 (4 ) 0. 01 21 (4 ) 0. 00 83 (2 ) 0. 00 87 (2 ) 0. 01 26 (3 ) 0. 01 70 (5 ) 0. 02 78 (7 ) 0. 02 02 (7 ) 0. 01 41 (5 ) 0. 01 68 (5 ) 0. 01 27 (4 ) 0. 01 27 (4 ) 0. 01 46 (5 ) 0. 01 91 (6 ) 0. 02 82 (9 ) 0. 02 3 1 (8 ) 0. 01 81 (6 ) 0. 01 27 (4 ) 0. 01 27 (4 ) 0. 01 41 (5 ) 0. 01 68 (5 ) 0. 01 78 (6 ) 0. 03 93 (1 4) 0. 02 78 (9 ) 0. 02 57 (9 ) 0. 02 52 (9 ) 0. 04 00 (1 6) 0. 05 92 (2 7) 0. 02 7 1 ( 1 5) 0. 03 69 (1 4) 0. 03 29 (1 2) 0. 02 32 (8 ) 0. 02 69 (9 ) 0. 02 28 (7 ) 0. 01 43 (5 ) 0. 01 49 (3 ) 0. 01 80 (4 ) 0. 02 16 (5 ) 0. 06 69 ( 19 ) 0. 04 31 (1 2) 0. 00 60 (2 ) 0. 00 50 (2 ) 0. 00 52 (2 ) 0. 00 51 (2 ) 0. 00 46 (1 ) 0. 00 58 (2 ) 0. 00 69 (2 ) 0. 00 64 (2 ) 0. 00 50 (2 ) 0. 00 73 (2 ) 0. 01 00 (3 ) 0. 00 57 (2 ) 0. 00 49 (2 ) 0. 01 11 (3 ) 0. 00 74 (2 ) 0. 00 57 (2 ) 0. 00 60 (2 ) 0. 00 72 (3 ) 0, 00 81 (2 ) 0. 01 00 (4 ) 0. 01 22 (5 ) 0. 00 70 (3 ) 0. 00 74 (3 ) 0. 00 67 (2 ) 0. 00 69 (2 ) 0. 00 75 (2 ) 0. 00 50 (2 ) 0. 00 62 (1 ) 0. 00 99 (2 ) 0. 00 49 (1 ) 0. 01 57 (4 ) 0. 00 78 (2 ) 0. 00 03 (3 ) 0. 00 09 (4 ) 0. 00 01 (3 ) - 0. 00 03 (3 ) - 0. 00 13 (3 ) - 0. 00 09 (4 ) 0. 00 02 (5 ) 0. 00 13 (4 ) - 0. 00 07 (4 ) - 0. 00 10 (3 ) - 0. 00 02 (3 ) - 0. 00 02 (3 ) - 0. 00 20 (3 ) - 0. 00 36 (4 ) 0. 00 24 (6 ) - 0 .0 02 9 (6 ) - 0. 00 04 (6 ) - O .o o0 0 (6 ) 0. 00 61 (1 0) 0. 00 70 (1 3) 0. 00 86 (8 ) 0. 00 62 (7 ) 0. 00 31 (5 ) 0. 00 54 (5 ) 0. 00 56 (5 ) 0. 00 15 (4 ) 0. 00 08 (2 ) - 0. 00 93 (1 5) - 0. 00 29 (3 ) - 0. 00 36 (3 ) - 0 .0 16 5 (8 ) 0. 01 18 (7 ) 0. 00 16 (2 ) 0. 00 12 (2 ) 0. 00 07 (2 ) 0. 00 05 (2 ) o. O o0 4 (2 ) 0. 00 12 (2 ) 0. 00 28 (2 ) 0. 00 21 (2 ) 0. 00 02 (2 ) - 0. 00 02 (2 ) - 0 .0 00 3 (2 ) 0. 00 16 (2 ) 0. 00 07 (3 ) - 0. 00 03 (2 ) 0. 00 28 (3 ) 0. 00 09 (3 ) 0. 00 27 (3 ) 0. 00 25 (4 ) 0. 00 24 (5 ) -0 .0 01 6 (9 ) - 0. 00 02 (3 ) 0. 00 02 (2 ) 0. 00 01 (2 ) - 0. 00 02 (3 ) 0. 00 03 (3 ) 0. 00 13 (2 ) 0. 00 26 (2 ) 0. 00 06 (1 ) 0. 00 15 (2 ) -0 .O OO 9 (1 ) - 0. 00 42 ( 3) 0. 00 70 (3 ) 0. 00 23 (3 ) 0. 00 09 (3 ) - 0. 00 01 (2 ) -0 .0 00 3 (2 ) -0 .0 01 4( 3) 2 0. 00 13 (4 ) * 0. 00 19 (3 ) 9 0. 00 08 (2 ) [ 0. 00 04 (3 ) 0. 00 01 (2 ) 7 -0 .0 02 1 (4 ) 8 0. 00 00 (4 ) g -0 .0 00 2 (3 ) 2 0. 00 12 (3 ) ; 0. 00 05 (6 ) g 0. 00 43 (4 ) Q I 0. 00 29 (4 ) - ’ 0. 00 34 (4 ) 2 0. 00 82 (6 ) 2 0. 01 36 (9 ) 0. 00 21 (8 ) 5 0. 00 39 (5 ) 7 0. 00 07 (3 ) 0. 00 07 (4 ) 2 0. 00 21 (5 ) 2 0. 00 12 (4 ) - 0. 00 01 (3 ) 0. 00 22 (2 ) 0. 00 21 (2 ) 0. 00 26 (2 ) 0. 02 1 1 (8 ) 0, 00 81 (4 ) 0. 01 79 c 5i 0. 05 28 i1 4j O. OI OO ( 2j 0. 00 91 (7 j 0. 00 20 ( 3j 0. 01 1 4 ( 6j 0 34 0 3 5 03 6 H 1 H 2A H 2B H 3 H 6A H 6B H 7A H 7B H 9 H 1 0 H 1 2A H 1 2B H 1 3A H 1 3B H 13 C H 1 4A H 1 4B H 15 A H 15 B H 1 5C H 1 7 H 1 9A H 1 9B H 20 A H 20 B H 21 A H 21 B H 21 C H 23 H 24 H 25 H 26 0. 64 93 (6 ) ’ 0. 33 44 (3 ) 0. 37 12 (2 ) 0. 17 0 (4 ) 0. 27 6 (4 ) 0. 14 4 (6 ) 0. 19 1 (3 ) 0. 06 2 (4 ) 0. 09 9 (4 ) - 0. 10 8 (4 ) -0 .1 24 (3 ) - 0. 20 6 (4 ) -0 .0 16 ( 3) 0. 25 2 (4 ) 0. 30 3 (4 ) 0. 30 9 ( 4) 0. 38 6 (4 ) 0. 30 7 (4 ) 0. 06 5 (4 ) - 0. 04 3 (5 ) - 0. 37 7 (5 ) - 0. 35 2 (5 ) - 0. 38 2 (5 ) 0. 18 3 (6 ) 0. 30 9 (5 ) 0. 25 3 (6 ) 0. 45 0 (6 ) 0. 36 9 (7 ) 0. 16 7 (9 ) 0. 01 3 (6 ) 0. 74 4 (5 ) 0. 48 1 (5 ) 0. 70 6 (4 ) 0. 59 3 (4 ) 0. 13 3 (7 ) 0. 10 97 (1 6) 0. 29 70 (1 0) 0. 50 61 (1 1) 0. 87 5 (6 ) 0. 65 4 (5 ) 0. 58 9 (8 ) 0. 45 4 (5 ) 0. 86 1 (5 ) 0. 75 5 (5 ) 0. 67 3 (6 ) 0. 85 1 (4 ) 0. 70 5 (6 ) 0. 58 8 (4 ) 1. 03 5 ( 6) 0. 95 1 (5 ) 0. 54 2 (5 ) 0. 64 4 (5 ) 0. 69 1 (5 ) 0. 42 9 (4 ) 0. 49 0 (6 ) 0. 69 1 (7 ) 0. 81 9 (6 ) 0. 83 9 (7 ) 0. 43 3 ( 7) 0. 28 8 (7 ) 0. 12 4 (8 ) 0. 07 4 (9 ) 0. 01 4 (9 ) 0. 07 3 (1 3) -0 .0 56 (1 0) 0. 08 1 (8 ) 0. 20 8 (6 ) 0. 26 0 (6 ) 0. 31 4 (5 ) 0. 42 0 (6 ) 0. 51 82 (4 ) 0. 14 69 (2 ) 0. 06 88 (2 ) - 0. 03 3 (3 ) - 0. 05 5 ( 3) - 0. 07 3 (4 ) 0. 06 4 (2 ) 0. 21 2 (3 ) 0. 29 5 (2 ) 0. 30 5 (3 ) 0. 28 8 (2 ) 0. 02 9 (3 ) 0. 03 5 (2 ) 0. 12 8 (3 ) 0. 21 2 (2 ) 0. 26 0 (2 ) 0. 21 6 (3 ) 0. 28 2 (3 ) 0. 20 5 (3 ) 0. 15 9 (4 ) 0. 23 9 (3 ) 0. 45 1 (4 ) 0. 56 4 (4 ) 0. 59 6 (4 ) 0. 56 8 (4 ) 0. 48 6 (5 ) 0. 36 5 (6 ) 0. 46 5 (5 ) 0. 40 8 (4 ) 0. 38 6 (3 ) 0. 29 3 (3 ) 0. 21 8 (3 ) 0. 07 8 (3 ) 0. 16 4 (2 ) 0. 12 0 (4 ) 0. 02 63 0. 01 38 0. 00 97 4. 0 (0 ) ( 8) 0. 09 40 (3 4) 0. 01 15 (3 ) 0. 01 46 (1 3) 0. 00 15 ( 4) 0. 01 73 (9 ) (3 ) 0. 01 43 (4 ) 0. 00 84 (2 ) - 0. 00 07 (3 ) -0 .0 01 8 (2 ) 0. 00 18 (2 ) (2 ) 0. 01 52 (4 ) 0. 00 64 (1 ) 0. 00 23 (2 ) 0. 00 16 (1 ) 0. 00 11 ( 2) 2. 8 (8 ) 7. 4 (1 5) 2. 7 (8 ) 2. 5 (8 ) 4. 2 (1 0) 1. 4 ( 6) 3. 6 (9 ) 0. 6 (6 ) 3. 9 (9 ) 2. 3 (7 ) 2. 4 (7 ) 3. 7 (9 ) 2. 9 (8 ) 2. 0 (7 ) 4. 6 (1 1) 8. 7 (1 3) 4. 6 (1 0) 6. 8 (1 2) 5. 8 (1 2) 6. 5 (1 3) 8. 0 (1 5) 7. 1 (1 5) 7. 1 (1 6) 13 .2 (2 5) 8. 7 (1 7) 7. 7 (1 5) 4. 9( 11 ) 5. 1 (1 1) 3. 6 (9 ) 2. 2 (7 ) 3. 5 (9 ) h ) 4 8 Q I N 0 0 W -4 W h + v z N -4 w 2704 HELVETICA CHIMICA ACTA - Vol. 62, Fasc. 8 (1979) - Nr. 273 circle diffractometer using graphite monochromated MoKa radiation (0.7 1069 A) and a variable speed o-scan. A total of 2647 reflections were measured in this fashion and after correction for Lorentz, polarization and background effects, 2466 (93%) were judged observed ( I Fo I 2 3 D (Fo)). A phasing model was achieved using a multi-solution, weighted tangent formula approach [22]. An E-synthesis of one of the more reasonable solutions showed a plausible 22 atom fragment and tangent formula recycling led to a model with all 36 non-hydrogen atoms. Full matrix least-squares refinements with anisotropic thermal parameters for the non-hydrogen atoms and isotropic hydrogens have currently converged to a standard crystallographic residual of 0.062 for the observed reflections2). A computer generated drawing, using the known absolute configuration, is shown in the Figure and the fractional coordinates and thermal parameters are in the Table. Discussion. - The results of the single crystal X-ray diffraction study of verrucarin B (2) are shown in the Figure. This study defined the 17s- and 18R- configuration of the C(17)-C (18) epoxide3). The macrocyclic ring is trans-fused on the epoxide, H-C( 17) and H,C-C (18) being on opposite sides of the epoxide. The configuration at C(18) is the same in verrucarin A (1) and verrucarin B (2). All other molecular parameters are generally in good agreement with those anticipated for this class of molecule. According to the X-ray analysis of verrucarin B (2), the 2,3-epoxy-anhydromevalonic acid moiety 14 possesses the 2 S , 3 R-configuration. On this basis and with reference to the earlier suggestion for the reaction sequence [2 I], the following mechanism for the biogenetic transformation of mevalonic acid (12) to verrucarinic acid (7) is proposed (Scheme 2). Cis-elimination of water yields trans-anhydromevalonic acid ( 13)4), which is epoxidized to the glycidic Scheme 2 nu CH3 cHx - HO I dWH HO / J H 12 13 J 2, All crystallographic calculations were done on a Prime 400 computer, operated by the Materials Science Center, Cornell University. The principal programs used were REDUCE and UNIQUE, data reduction programs, M . E. Leonowiez, Cornell University, 1978; BLS, block diagonal least squares refinement, K. Hirotsu, Cornell University. 1978; ORFLS (modified), full matrix least squares, W. R. Busing, K . 0. Marfin and H. S. Levy, Oak Ridge, ORNL-MT 305; ORTEP, crystallo- graphic illustration program, C. Johnson, Oak Ridge, ORNL-3794, BOND, structural parameters and errors. K. Hirotsu, Cornell University, 1978; MULTAN-76, direct methods and fast Fourier transform, G. Germain, P. Main and M. Woolfson, University of York. These C-atoms correspond to C(2’) and C(3’) in the usual numbering system. The anhydromevalonic acid moiety of verrucarin J (3) very likely possesses trans- and not cis- configuration as anticipated earlier [5]. 3, 4, HELVETICA CHIMICA ACTA - VOI. 62, Fasc. 8 (1979) - Nr. 273 2705 acid 14. Subsequent cleavage of the oxirane and a 1,2-hydride shift from C(2) to C(3) with inversion of chirality at C(3) leads to the keto acid 15. The last step in the formation of (2S,3R)-verrucarinic acid (7) is the stereospecific reduction of 2-dehydroverrucarinic acid (15). The result of the X-ray analysis of verrucarin B (2) suggests that the structural moiety of the closely related microbial metabolite roridin D [8], which also contains an epoxy-anhydromevalonic acid (14) fragment, possesses the absolute configuration shown in 16. H H O Y 0 16 Roridin D The support of these investigations by the Schweizerischer Nationalfonds zur Forderung der wissenschuftlichen Forschung, (Projects No. 2.435.0.75 and 2.629.0.76) and by Sundoz A G., Basel, is gratefully acknowledged. The Cornell authors gratefully acknowledge support by N I H - N C I . REFERENCES [I] 35th Commun.: W. Breitenstein & Ch. Tamm, Helv. 61, 1975 (1978). (21 J. Gutzwiller & Ch. Tumm, Helv. 48, 177 (1965). [3] E. Harri, W. Loefler, H. P. Sigg, H. Stahelin, Ch. Stoll, Ch. Tumm & D. Wiesinger, Helv. 45, 839 [4] J . Gutzwiller & Ch. Tamm, Helv. 48, 157 (1965); A. T. McPhuil & G.A. Sim, J. chem. SOC. (C) 1966, [5] E. Fetz, B. Bdhner & Ch. Tumm, Helv. 48, 1669 (1965). [6] W. Ziircher & Ch.,Tumm, Helv. 49,2594 (1966). 171 B. Bohner& Ch. Tamm, Helv. 49,2527 (1966). [8] B. Bdhner & Ch. Tumm, Helv. 49,2547 (1966). 191 P. Truxler, W. Ziircher & Ch. Tumm, Helv. 53,2071 (1970). [lo] P. Traxler & Ch. Tamm, Helv. 53, 1846 (1970). [ I l l Ch. Tumm, Progr. Chemistry Org. Natural Prod. 31, 63 (1974); Ch. Tumm, ‘Chemistry and Bio- synthesis of Trichothecenes’ in ‘Mycotoxins in Human and Animal Health’, Edit. by J. V. Rodricks, C.V. Hesseltine 6t M.A. Mehlman, Pathotox Publishers Inc., Park Forest South, Illinois, U.S.A. 1977,209-228. (1962); B. Bohner, E. Fefz, E. Harri, H. P. Sigg, Ch. Stoll& Ch. Tumm, Helv. 48, 1079 (1965). 1394. [12] J. Gutzwiller, R. Muuli, H. P. Sigg & Ch. Tamm, Helv. 47,2234 (1964). [ 131 W. 0. Godtfredsen, J . F. Grove & Ch. Tumm, Helv. 50, 1666 (1967). [I41 R. M. Eppley, E. P. Muzzola, R. J. Highet & W.J. Bailey, J . org. Chemistry 42, 240 (1977). [I51 W. Breitenstein & Ch. Tumm, Helv. 60, 1522 (1977). [I61 H. Minuto, T. Katayuma& K. Tori, Tetrahedron Letters 197j3 2579. [I71 M. Matsumoto, H. Minuto, K. Tori & M. Ueyamu, Tetrahedron Letters 1977, 4093; M. Mutsumoto, [18] S.M. Kupchan, B.B. Jurvis, R.G. Duiley, jr., W. Bright, R.F. Bryan & Y. Shizuri, J. Amer. chem. [I91 R. Achini, B. Miiller & Ch. Tumm, Chem. Commun. 1971, 404. [20] B. Miiller, R. Achini & Ch. Tamm, Helv. 58,453 (1975); 8. Muller & Ch. Tamm, Helv. 58,483 (1975). [21] R. Achini, B. Miiller & Ch. Tamm, Helv. 57, 1442 (1974). [22] J. P. Declercq, G. Germain & M. M. Woolfon, Acta crystallogr. A 31,367 (1975) and ref. therein. H. Minuto, N. Uotuni, K. Matsumoto & E. Kondo, J. Antibiotics 30,681 (1977). SOC. 98,7092 (1976).