Donald W. Cameron

Detection of brassinosteroids in pollen of Lolium perenne L. by immunocytochemistry

Bioactive brassinosteroids have been localized in developing and mature pollen of anhydrously fixed rye-grass (Lolium perenne) by immunocytochemistry using polyclonal antibodies to castasterone generated in rabbits. Tricellular pollen fixed by freeze-substitution was also labelled in the starch granules. Study of the developmental sequence of the pollen through the microsporocyte, microspore, bicellular and tricellular stages showed that the brassinosteroids were increasingly sequestered in starch granules as the amyloplasts matured, supporting the view that these are storage organelles for these potent plant growth promoters. In bicellular pollen, heavy labelling was seen in the zone within 0.5 μm of the starch granule, where stromal tissue remains. Thus, the stroma may be the site of synthesis of these compounds. During aqueous fixation, the brassinosteroids leached from the starch granules of tricellular pollen, indicating that they would be quickly available after imbibition to influence the physiology of germinating pollen. The results from high-performance liquid chromatography of dansylaminophenylboronates from partially purified extracts of freshly dehisced tricellular pollen of rye-grass showed 25-methylcastasterone may be a minor component, together with two unknown peaks. No specific binding of brassinolide to any soluble proteins extracted from tricellular rye-grass pollen was observed using the antibodies in gel electrophoresis or enzyme-linked immunosorbent assays.

Thermal 1,5-rearrangement of a silyl group from oxygen to carbon

Abstract Trialkylsilyl ethers of 1,1-dioxygenated butadienes, substituted at position 3 by electron releasing substituents, undergo thermal rearrangement with 1,5-migration of the silyl group from oxygen to carbon.

Synthesis of stentorin

Abstract The two symmetrical structures 1 and 2 proposed for the photodynamic pigment stentorin have both been synthesised, thereby establishing the correctness of structure 1.

1,4-anthraquinonoid dienophiles applicable to synthesis of linear tetracycles

Abstract Derivatives of 1,4-anthraquinones (3), (21) are shown to be good dienophiles for achieving strongly regiocontrolled synthesis of linear tetracycles, a property greatly enhanced by their ease of formation and of subsequent replacement of the chloride.

Stereochemistry and cycloaddition of 1,1,3-trioxy butadienes from β-keto esters

Abstract Spectroscopic analysis of the 1,1,3-trioxy dienes (1), (2) shows them to possess ( Z )-stereochemistry, contrary to several literature assignments; characterisation of derived cycloadducts and crystallographic analysis of one of them (20) establishes endo cycloaddition.

Synthesis of tetracenomycins

Tetracenomycins D, A2, B1 and B2 (2)–(5) have been synthesised for the first time, by an efficient, regioselective sequence based on cycloaddition methodology; the ambiguity that existed for tetracenomycins B1 and B2 has thereby been resolved in favour of structures (4a) and (5b) respectively.

Synthesis of specifically O-alkylated anthraquinones by cycloaddition

Abstract Cycloadducts from naphthoquinonoid dienophiles and 1-methoxy-1-trimethylsilyloxy butadienes undergo controlled aromatisatlon to form chiefly α-hydroxy- or α-methoxy-anthraquinones; this has led to synthesis of several natural O -methyl polyoxyanthraquinones.

Synthesis of the naphthacenequinone SS-228R

Abstract The two structures (1) and (2) proposed for the naphthacenequinone SS-228R have both been synthesised, thereby establishing the correctness of structure (2).

Iridoids of garrya elliptica as plant growth inhibitors

Abstract Extracts from catkins of Garrya elliptica inhibit the growth of wheat embryos. The components responsible for this activity have been identified as the iridoids geniposide and geniposidic acid together with their aglucones.

Synthesis of a natural polychloro dinaphthofuran quinone

Abstract The hexachloro dinaphthofuran quinone (1), the only natural example of this ring system has been synthesised for the first time.