itution step. The most beneficial preferred conformation on the benzylic carbenium ion in LTE4 Purity & Documentation outcome is often explained by a preferred conformation of your benzylic carbenium ion in theO-methylation offered selectivities were obtained using the tert-butylamide. Subsequent substitution step. The bestmethoxy derivative 31, convertedthe tert-butylamide. Subsequent acid 32 below standthe selectivities have been obtained with in to the N-Boc-protected amino O-methylation offered the methoxy derivative 31, IP Species converted into the N-Boc-protected amino acid 32 below ard situations. typical circumstances.Scheme 7. Synthesis of protected -methoxy phenylalanine 32 (creating block 4 ). Scheme 7. Synthesis of protected -methoxy phenylalanine 32 (building block ).Finally, the unsaturated amino acid was obtained through an asymmetric chelate enolate Lastly, the unsaturated amino acid 7 was obtained through an asymmetric chelate enolate Claisen rearrangement, created by Kazmaier et al. (Scheme eight) [54,55]. TrifluoroaClaisen rearrangement, developed by Kazmaier et al. (Scheme 8) [54,55]. Trifluoroacetyl cetyl (TFA)-protected glycine crotyl ester deprotonated and converted into a chelated alu(TFA)-protected glycine crotyl ester 33 was 33 was deprotonated and converted into a chelated aluminum ester enolate, which within the presence of quinidine a [3,3]-sigmatropic reminum ester enolate, which inside the presence of quinidine underwentunderwent a [3,3]-sigmatropic rearrangement to amino acid 34 with acid yield and enantioselectivity. Epimerarrangement to unsaturated unsaturated amino good34 with excellent yield and enantioselectivity. in the -stereogenic center was avoided by was avoided by 1st the Boc-protected ization Epimerization on the -stereogenic center very first converting 34 intoconverting 34 into ester 35 and after that, within a second step, into the corresponding phthaloyl-protected derivative the Boc-protected ester 35 and then, in a second step, in to the corresponding phthaloyl36. A direct epimerization-free conversion (34 to 36) was not achievable. Ozonolysis of your protected derivative 36. A direct epimerization-free conversion (34 to 36) was not attainable. Ozonolysis in the double bond and subsequent Wittig reaction made protected amino acid 37, ultimately converted in to the Fmoc-protected acid 38.Mar. Drugs 2021, 19,Lastly, the unsaturated amino acid was obtained by way of an asymmetric chelate enolate Claisen rearrangement, developed by Kazmaier et al. (Scheme eight) [54,55]. Trifluoroacetyl (TFA)-protected glycine crotyl ester 33 was deprotonated and converted into a chelated aluminum ester enolate, which in the presence of quinidine underwent a [3,3]-sigmatropic rearrangement to unsaturated amino acid 34 with great yield and enantioselec11 of 27 tivity. Epimerization with the -stereogenic center was avoided by initial converting 34 in to the Boc-protected ester 35 and after that, inside a second step, in to the corresponding phthaloylprotected derivative 36. A direct epimerization-free conversion (34 to 36) was not attainable. Ozonolysis on the double bond and subsequent Wittig reaction created acid 37, amino double bond and subsequent Wittig reaction developed protected aminoprotectedfinally acid 37, ultimately converted into the acid 38. converted in to the Fmoc-protectedFmoc-protected acid 38.Scheme 8. Synthesis of protected dehydroamino acid 38 (building block 7 ). Scheme 8. Synthesis of protected dehydroamino acid 38 (developing block ).Soon after the preferred building blocks were produced, the synthesis of cyclomarin C and es
