Thermolabile intermediate

The utilization of pericyclic reactions of thermolabile intermediates has been extended to 7-methylcyclooctatetraene, a pheromone from the brown alga Cutleria multifida. Boland and Pohnert have reported the electrolytic ring closure of l,3Z,5Z,7E-nonatriene to afford the cyclooctatetraene derivative [52]. The biomimetic synthesis of this pheromone lends additional support to the suggested use of pericyclic reactions in the biosynthesis of the algal gynogametes. 

Homogenates of MetruUum senile, possibly the world s most common large sea anemone, yield extracts that are powerfully hemolytic for washed mammalian erythrocytes (22). The active substance, metridiolysin, is a protein of molecular weight approximately 80,000. In contrast to the sphingomyelin-inhibitable toxins, metridiolysin is an acidic protein having a pi of about 5. It is thermolabile and is inactivat by proteolytic enzymes. The optimal pH for hemolysis is between 5 and 6, and at pH 8 the lysin is inactive. It can be dissociated into two subunits of unequal size. Besides being cytolytic in vitro, metridiolysin is lethal when injected intravenously into mice. As shown in Table IV erythrocytes from the horse or dog are about a hundred times as sensitive to lysis as those from the mouse, and erythrocytes from other animals tested are intermediate in sensitivity. 

The synthetic utility of the ring expansion reaction was demonstrated by its application to the synthesis of thermolabile thiepins. When the diazo compound (66) obtained from benzo[c]thiopyrylium salt 65 was treated with palladium catalyst under the same conditions as in the case of 63, the product isolated was ethyl 2-naphthoate (68)48). The plausible reaction pathway is one comprising i) decomposition of 66 to the corresponding carbene intermediate, ii) ring expansion to the... 

Kang, S. S.,Zhou, J., Wong, P.W., Kowalisyn, J., and Strokosch, G. (1988)Intermediate homo-cysteinemia a thermolabile variant of methylenetetrahydrofolate reductase. American Journal of Human Genetics. 43, 414-421. 

Reactivity with Diazo Oxides and Azides. Diazo oxides, e.g. 2,6-di-f0rf-butyl-4-diazo-2,5-cyclohexadiene-l-one (184, R = terr-butyl) or 2,6-diphenyl-4-diazo-2,5-cyclohexadiene-l-one (184, R = phenyl) are thermolabile and photolabile. Car-benes 185 are formed from 184 as reactive intermediates. The process proceeds in a one-step mechanism in which the carbene species reacts in the singlet state [238], The attachement of 185 to saturated hydrocarbon chains proceeds via insertion in C—H bond during processing. LDPE and PP were modified in this way [239, 240]. Poly(oxymethylene) was modified similarly. 

C, FA extraction was slightly decreased. The decreased recoveries obtained were not a result of the thermal instability of the unsaturated FAs at 150°C as the yield of extracted saturated FAs decreased at least to the same extent as that of the unsaturated FAs. It seems more likely that the extraction efficiency started to decrease at temperatures above 120°C [15]. Whether thermolabile species are involved or an increased extractant density has an adverse effect on the extraction efficiency, intermediate temperatures should be used to ensure reliable extraction [16]. 

Consequently most examples performed so far have been outlined in a two-step, one-pot procedure. Several intermediate aminohexatrienes (4) are so thermolabile that isolation fails or becomes too wasteful. 

Thermolabile 2,2,5,5-tetrasubstituted A3-l,3,4-selenadiazolines (83) are useful in the preparation of sterically very crowded alkenes (Scheme 16). Episelenides (84), which provide access to the alkenes by ready loss of selenium, are postulated as the intermediates in the thermal decomposition of (83) <76JCS(P 1 )2079>. 

Kang SS, Zhou J, Wong PW, Kowahsyn J, Strokosch G. Intermediate homocysteinemia a thermolabile variant of methylenetetrahydrofolate reductase. Am J Hum Genet 1988 43 414-21. 

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