Aglycons lactonization

Neomethymycin (12, R = H, R = OH), an isomer co-produced with methymycin, is the product of hydroxylation at C-12 rather than C-10 of the lactone (34,35). The corresponding aglycone, neomethynoHde (13, R = H, R = OH), was isolated with methynolide from broths of S. vene elae (36). The stereochemistry of 12(R)- for neomethynoHde was estabHshed by total synthesis (37). YC-17 (12, R = R = H), also found in broths of S. vene elae is a possible precursor of methymycin and neomethymycin. The hydroxyl groups at C-12 and C-10 are probably added as late steps in the biosynthesis (38). 

A few neutral 16-membered macroHdes have been isolated. The stmcture of chalcomycin (54, R = CH3, R = OH), produced by S. bikiniensis was estabhshed as a 16-membered lactone having two neutral sugars, D-chalcose (7) and D-mycinose (9, R = R = OH3) (293—295). Its aglycone resembles that... 

It is known that the presence of the 143-hydroxyl group and a sugar at the 3 position are absolute requirements for activity. A modified drug actodigin (100) demonstrates that reversal of the lactone 17 is consistent with activity. Reduction of digitoxigenin 91, the aglycone of digitoxin... 

THF/liq. NH3, followed sequentially by oxidation and base-induced double bond isomerization, provides butenolide 33, a compound that possesses the lactone system of the steroidal cardiac aglycones. 

The utility of RCM methodology for the synthesis of open-chain building blocks from a,fi-unsaturated d-lactones is exemplified by the partial syntheses of Cossy aimed for (+)-methynolide (the aglycon of the methymicin family of macrolide antibiotics) [45], and the anticancer agent discodermolide [46], as well as during a recent total synthesis of the highly cytotoxic marine natural depsipeptide apratoxin A by Forsyth and Chen [47]. 

As reported for all pentasaccharides from sweet potato (64, 86), pure compounds 232 and 233 were also submitted to sapoiufication yielding simonic acid B (87). The liberated fatty acids were identified as isobutyric, (25)-methyIbutanoic, -decanoic, -dodecanoic, and cinnamic acids. The site of lactonization by the aglycone in the macrocyclic unit was placed at C-2 of the second saccharide. The position of the ester linkage on the macrocyclic unit was C-2 of the terminal rhamnose. The acylations were identified as follows for the macrocyclic unit at C-2 of the third saccharide (n-dodecanoic acid), and at C-3 and C-4 of the branched... 

Aedes aegyptl, Trlbollum castaneum, Perlplaneta amerlcana, and Phthormea operculella (165). Two other sesquiterpene lactones, coronopllln and tetraneurln-A (166), and 34 flavones (19 glycosides and 15 aglycones) have been Isolated from Parthenlum species (167) ... 

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