Bernard Crammer

Plant-growth regulators derived from the sweetener stevioside

A series of isosteviol derivatives such as aromatic esters and amino acid amides were synthesized. Their effects on seed germination and root elongation of the crop plants, Capsicum annuum, Lens culinaris medicus, Lycopersicon esculentum, Trifollium spp. and Triticum vulgare, were studied. The derivatives could be arranged into four groups: (1) seed germination inhibitors (2) root elongation inhibitors (3) root elongation inducers (4) general inhibitors.

Mechanistic study of the thermal acid-catalysed rearrangement of trans-methyl chrysanthemate to lavandulyl derivatives

trans-Methyl chrysanthemate (17) under acid conditions at room temperature rearranged to the lavandulyl esters: methyl trans-5-methyl-2-propen-2-ylhex-3-enoate (18) and methyl trans-5-methyl-2-(2-hydroxypropan-2-yl)hex-3-enoate (19) which was formed by a cyclopropylcarbinyl–homoallyl rearrangement. Both (18) and (19) further isomerise and dehydrate to the stable methyl trans-5-methyl-2-propan-2-ylidenehex-3-enoate (20). Under similar acidic conditions, (18) and (19) each give a mixture of lavandulyl esters and (17); minor amounts of side products, methyl trans-5-methylhex-3-enoate (21), methyl trans-5-methyl-2-(2-methoxypropan-2-yl)hex-3-enoate (22), methyl cis-5-methyl-2-propen-2-ylhex-2-enoate (23) were detected after some time. Acid methanolysis of (17) gave a substantial amount of (22) and its isomer, methyl 2,2-dimethyl-3-(2-methoxypropan-2-yl)cyclopropanecarboxylate (26). There was also found in low concentration, methyl trans-5-methyl-2-propan-2-ylhex-3-enoate (24) and methyl 5-methyl-2-propan-2-ylidenehexanpate (25) possibly the result of a hydride transfer from the solvent. Deuterium exchange was observed in the isobutenyl side-chain of (17) and the isobutenyl moiety of (18) and (19). At 130°C under similar acidic conditions a mixture of unsaturated γ- and δ-lactones was obtained from (17). The principal lactone was dihydro-5-propan-2-yl-3-propan-2-ylidenefuran-2(3H)-one (29). Mechanisms for the formation of these products are discussed. The fact that lavandulyl derivatives were obtained may shed new light on the biogenesis of chrysanthemic acid in plants.

Studies of chrysanthemic acid derivatives: catalysed reactions of 3-(2-hydroxy-methyl-3,3-dimethylcyclopropyl)-2-methylpropanol and formation of a novel eight-membered cyclic sulphite

Acid catalysed reaction of the cyclopropanediol (3) derived from cis-chrysanthemic acid cis-(1) afforded, depending on the reaction conditions, 3-vinyl-2,2,5,5-tetramethyltetrahydrofuran (4) and 4,4,7,7-tetramethyl-3-oxabicyclo[4.1.0]heptane (5). On treatment with thionyl chloride–pyridine complex there was obtained in addition the eight-membered cyclic sulphite, 6,6,9,9-tetramethyl-3,5-dipxa-4-thiabicyclo[6.1.0]nonane 4-oxide (6). X-Ray analysis confirms a boat-chair conformation with the SO group trans to the cyclopropane ring and in an equatorial situation. Thermal reaction of (6) gave either (4) or a mixture of (5), cis-chrysanthemol (7), and cis-isochrysanthemol (8).