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summary Ozone (O3) in ambient air was investigated as a possible cause of visible damage to leaves of white clover (Trifolium repens L.) in agricultural areas of Switzerland. Differences in the sensitivity of five commonly mown cultivars were studied, namely Ladino Sacramento, Ladino California, Alban, Sonja and Milkanova. Plants were grown in pots and exposed to O3 using three different experimental systems: (i) exposure to ambient air, (ii) exposure in open‐top chambers to filtered air, unfiltered air, or unfiltered air to which O3 was added from 09.00 until 17.00 h during a four‐day period, (iii) exposure under controlled environmental condition to filtered air with or without O3 added daily. Occurrence of injury symptoms on field‐grown plants was recorded during the summers of 1987 and 1988. Ozone exposure produced visible injury expressed as small necrotic flecks on the tipper leaf surface. Irrespective of the experimental system used, the following order in O3 sensitivity was observed: L. Sacramento ≤ L. California ≪ Alban ≤ Sonja ≤ Milkanova. Injury symptoms were seen when plants were exposed to ambient O3 or to unfiltered air in open‐top chambers, but not in charcoal‐filtered air. In ambient air, symptoms in the most sensitive cultivars appeared after episodes with 1‐h maximum concentrations of above 120‐140μg m−3 occurring on several consecutive days. The symptoms of injury could be reproduced in controlled‐environment fumigation experiments using concentrations comparable to those observed in ambient air. Plants of the different cultivars grown under controlled environmental conditions did not differ in superoxide dismutase or peroxidase activity, or in the content of fructose, sucrose or glucose. Differences in O3−sensitivity between cultivars were related to differences in stomatal density and to some degree to the length of the stomatal pore. Stomatal densities were related to leaf conductance, transpiration, and rate of water loss by excised leaves. Leaves of Milkanova (resistant) had higher 313values than L. California (sensitive). Compared with filtered air, exposure to unfiltered ambient air or O3–amended air in open‐top chambers caused a change in δ13 value in leaves of L. California (sensitive), but not in leaves of Milkanova (resistant). It is concluded that ambient levels of O3 in Switzerland can be sufficient to produce visible leaf injury in sensitive white clover cultivars characterized by a high gas‐phase conductance of the leaves, that the isotopic composition of leaf tissue could be used as an indicator of O3 sensitivity in different cultivars, and that ambient levels of O3 can change the isotopic composition of the leaf tissue in sensitive species.

Thermolysis of the 1,2-bis(glucosylalkynyl)benzenes 6 and 16 was studied to evaluate the effects of intramolecular H-bonding on the activation energy of the Bergmun-Musumune-Sondheimer cycloaromatization, and to evaluate the use of the cycloaromatization for the synthesis of di-glycosylated naphthalenes. The dialkynes were prepared by cross-coupling of the 0-benzylated or 0-silylated glucosylalkynes 1 and 4 (Scheme I). Thiolysis of the known 1, or acetolysis of 1, followed by deacetylation (+ 2 -+ 3) and silylation gave 4. Cross-coupling of 1 or 4 with iodo-or 1,Zdiiodobenzene depended upon the nature of the added amine and on the protecting group, and led to the mono-and dialkynylbenzenes 5 and 6, or 12, 13, and 15, respectively. The benzyl ethers 5 and 6 gave poor yields upon acetolysis catalyzed by BF,-OEt2, while Ac,O/CoCl2.6 H,O transformed 6 in good yields into the regioselectively debenzylated 10. Desilylation of 7 and 13 gave the alcohols 8 and 14, respectively. Thermolysis of 6 in PhCl gave 22 and 23, independently of the presence or absence of 1,4-cyclohexadiene; 23 was formed from 22 (Scheme 2). Acetolysis of 22 gave the hexaacetate 24 that was completely debenzylated by thiolysis, yielding the dial 26 and truns-stilbene, evidencing the nature and position of the bridge between the glucosyl moieties (Scheme 3). Thiolysis of 22 yielded the unprotected 2,3-diglucosylnaphthalene 28, a new type of C-glycosides. Depending upon conditions, hydrogenation of 22 led to 29 (after acetylation), 30, or 32. NMR and particularly NOE data evidence the threo-configuration of the bridge. The structure of 23 was confirmed by hydrolysis to the diol34 and diphenylacetaldehyde, and by correlation of 23 with 22 via the common product 31. Formation of 22 is rationalized by a Eergmun cyclization to a diradical, followed by regioselective abstraction of a H-atom from the BnO-C(2) group, and diastereoselective combination of the doubly benzylic diradical (Scheme 4 ) . While thermolysis of 3 in EtOH sets in around 140°, 16 did not react at 160" and decomposed at 180-220". No evidence for intramolecular H-bonds of 16, as compared to 14, were found.Introduction. -We have described an approach to study inter-and intramolecular H-bonds of celluloses, based on a comparison of cello-oligosaccharides to analogues where the glycosidic 0-atom is replaced by butadiynediyl moieties [ 1-31. Attaching cello-oligosaccharides and their analogues in a parallel or antiparallel orientation to a scaffold should enhance the interaction between individual saccharide chains, and contribute to define and rationalize the differences between cellulose I and I1 [4][5][6]. Benzene is among the simplest scaffolds to which C-alkynylated saccharides can be attached, but the bond angle of 60" may disfavor the interaction of the glycosyl units in ortho-disubstituted benzene derivatives.We wondered if the Bergman-Masamune-Sondheimer rearrangement [7-111 of protected and unprotected 1,2-bis(2'-glycosylalkynyl)benzenes will lead to 2,3-diglycosylated naphthalenes...

A new oligonucleotide analog, bicyclo[3.2.1]-amide-DNA was synthesized. A homo-adenylate sequence of this analog, efficiently forms hetero-duplexes with complementary natural DNA and RNA. The corresponding homo-thymidylate sequence, however, does not base-pair to complementary DNA and RNA, but forms a stable duplex with the homo-adenylate oligomer of the same backbone type. The structure of this duplex is virtually enantiomeric to that of a natural B-DNA, as inferred from CD-spectroscopy.DNA-analogs are of interest as potential antisense agents in medicinal chemistry, and as tools in molecular biology. 1 Despite considerable efforts made over the recent years, the design of DNA-analogs with taylor-made biological and chemical properties still remains a challenge. With the aim of investigating the structural role of the furanose unit in RNA and DNA we recently designed and synthesized the analog bicyclo[3.2.1]-DNA 2 ( Figure 1). Figure 1 Structures of DNA, bicyclo[3.2.1]-DNA and bicyclo[3.2.1]amide-DNA In this analog the pentofuranose unit of DNA is replaced by a structurally rigid backbone unit that emulates a backbone conformation of the B-type, to which the bases were attached via a flexible, open-chain oxymethylene linker unit. Bicylo[3.2.1]amide-DNA is a related analog in which the bases are attached via an amide linker to the otherwise identical sugar scaffold. Here we describe the successful synthesis and the first pairing properties of bicyclo[3.2.1]-amide oligomers of the bases thymine and adenine. 3The monomeric building blocks 8 and 9 of bicyclo[3.2.1]amide-DNA, suitable for solid-phase oligonucleotide synthesis, were synthesized starting from the bicyclic amine 1 (Scheme 1) that was prepared earlier in our laboratory. 4 Coupling of thymin-1-yl acetic acid 5 with 1 using ethyl-N,N-dimethylaminoethyl carbodiimide (EDI) as the coupling reagent in DMF gave the nucleoside analog 2 (80%) that was subsequently tritylated with 4,4'-(dimethoxy)trityl triflate 6 to give 4 in high yield. Desilylation of 4 with Bu 4 NF in THF afforded 6 (83%) that was finally converted to the phosphoramidite 8 in 86% yield. The synthesis of the adenine containing nucleoside analog 3 (48%) was somewhat more cumbersome in that the mixed anhydride between N 6 -benzoyladen-9-yl acetic acid and isobutyl chloroformate had to be used to effect coupling to 1. The remaining reaction sequence 3 → 5 → 7 → 9 was performed as described for the thyminyl series in an overall yield of 22%. 7 Scheme 1 Reaction conditions: a) (2):1-Thy-CH 2 COOH (1.2 eq.), EDC (1.4 eq.), DMF, r.t., 5h, 80%; (3): 9-Bz 6 ade-CH 2 COOH (1.5 eq.), N-methyl morpholine (10 eq.), ClCOOiBu (1.5 eq.), DMF, 0°C, 1 min., then 1 (1 eq.) in DMF, r.t., 16h, 48%; b) DMT-OTf (2-4 eq.), pyridine, 50-60°C, 3-5h, 90% (4), 68% (5); c) Bu 4 NF (2 eq.), THF, r.t., 12-16h, 83% (6), 88% (7); d) ClP(OCH 2 CH 2 CN)N(iPr) 2 (3 eq.), (iPr) 2 NEt (6 eq.), THF, r.t., 3h, 86% (8), 75% (9).The phosphoramidite building blocks 8 and 9 were then used for the automated solid-phase assembly of oligonu...

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