Convertible bonds features, basic

Standard retrosynthetic manipulation of PGA2 (1) converts it to 5 (see Scheme 2). A conspicuous feature of the five-membered ring of intermediate 5 is the /(-keto ester moiety. Retrosynthetic cleavage of the indicated bond in 5 furnishes triester 6 as a potential precursor. Under basic conditions and in the synthetic direction, a Dieck-mann condensation4 could accomplish the formation of a bond between carbon atoms 9 and 10 in 6 to give intermediate 5. The action of sodium hydroxide on intermediate 5 could then accomplish saponification of both methyl esters, decarboxylation, and epi-merization adjacent to the ketone carbonyl to establish the necessary, and thermodynamically most stable, trans relationship between the two unsaturated side-chain appendages. 

Pauling and Corey (1599) made the point that under certain conditions globular proteins can be converted to forms similar to j8-keratin, and on this basis they proposed the a-helix as a basic feature in fRe structure. Perutz s x-ray work (256, 1614) shows that parts of horse hemoglobin may have this structure. Ambrose and Elliott (35) present some IR work on globular proteins in a paper which particularly stresses the functions of H bonds. 

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