Leucic acid

Note that we have used the following notation for hydroxy acids in this section, -O-Gly for the glycolic acid residue -0CH2C(0)-, likewise -O-Ile is the isoleucic acid residue -OCH(CHMeEt)C(0)-, -O-Leu is the leucic acid residue -0CH(iBu)C(0)-, -O-Phe is the (3-phenyllactic acid residue -0CH(Bzl)C(0)-, and -O-Phg is the phenylglycolic acid residue -OCHPhC(O)-. 

In 1959 Shchukina et a I. 56 showed that the addition of pyridine to DCC increases the yield (65-85%) of depsipeptides constructed from Z-protected amino acids and serine, threonine, or salicylic acid derivatives. The ferf-butyl ester of Af-(benzyloxycarbonyl)-leucylleucic acid (Table 2) was prepared in 60% yield under the same conditions of addition using a 2 molar excess of pyridine to carbodiimide. 57 The DCC/pyridine technique was successfully utilized in the ring closure between ()-alanine and leucic acid residues during the synthesis of the cyclic hexadepsipeptide destruxin B.[58 Under this modified approach the... 

Smidt and Langner111"1 in their synthesis of the natural calcium blocker leualacin utilized the Mitsunobu reaction for the construction of the linear depsipeptide N-(tert-but oxycarbony I) -(3-alanyl-O-D-leucic acid benzyl ester in 69% yield. Higher yields (94-96%) were reported for two didepsipeptide units N-(/er/-butoxycarbonyl)-./V-methylleucyl-D-lactic acid diphen-ylmethyl ester and iV-(/er/-butoxycarbonyl)-yV-methylleucyl-D-phenyllactic acid diphe-nylmethyl ester in the course of the total synthesis of the anthelmintic cyclooctadepsipeptide PF1022A based on the Mitsunobu reaction.1102 ... 

This depsipeptide was synthesized on a Pam resin, following the machine-assisted protocol described above, and introducing leucic acid in place of leucine at position 12. The cycles shown in Table 18.1 were performed. 

Hydroxy-4-rTrethylperrtarroic acid, (S) 7-Leucic acid C6H12O3 13748-90-8 132.167 orth (eth) 81.6 vs HjO, eth, EtOH... 

Frankland 1863. Frankland [9] was more successful when he investigated the reaction of diethylzinc with ethyl oxalate. He isolated the ester of an acid which had the same molecular formula as leucic acid , 2-hydroxyhexanoic acid. Apparently only one of the reactive sites of the oxalic acid ester was attacked by the organometallic reagent ... 

Frankland and Duppa 1865, Two years after his publication of the synthesis of leucic acid , Frankland, together with Duppa, reported a crucial improvement of the reaction of diethylzinc with oxalic ester. 

Once again no solvent was used in this reaction when a resinous mass was formed in the reaction vessel the reaction was considered to be finished and after hydrolysis leucic acid ether was distilled. 

Hydroxy-4-methylpentanoic acid, (S)- /.-Leucic acid C6H-12O3 13748-90-8 132.157 orth (eth) 81.5 vs H2O, eth, Eton... 

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