Synthesis of α-amino acids with β,γ-unsaturated side chains

Practical Syntheses of Both Enantiomers of Cyclopropylglycine and of Methyl 2‐Cyclopropyl‐2‐N‐Boc‐iminoacetate

“…The oily residue solidified upon standing to give the N-Boc-protected ester rac-9 as a colorless waxy solid; yield: 18.5 g (98%); mp 49 8C. 1 Methyl rac-2-(N-Benzyloxycarbonylamino)-2-cyclopropylacetate (rac-10) [26] This ester was prepared as described for rac-9, except that Cbz-OSu (N-benzyloxycarboxysuccinimide) was used instead of Boc 2 O. rac-10: oxime 7 (1.18 g, 9.13 mmol) was reduced with the activated zinc powder (see general remarks on reagents and chemicals, 4.78 g, 72.63 mol) in AcOH (27 mL) as described for rac-9, and the obtained glassy solid was covered with MeOH (10 mL). In a separate flask, a mixture of MeOH (20 mL), and SOCl 2 (5 mL) was prepared at -10 8C.…”

Functionalizing Glycine Derivatives by Direct CC Bond Formation

“…It should be noted that the existing methods to synthesize b,g-alkynyl a-amino acid derivatives requires the coupling of a-halo glycinates with alkynyltin reagents under refluxing conditions, [11] alkynylmagnesium reagent at À78 8C, [12] or transition-metal catalyzed alkynylation of a-imino esters. [13] Pre-functionalizations of amino acid derivatives at the aposition are essential in all cases.…”

Asymmetric Synthesis of α‐Allenylglycines

“…[1,2] a-Allenylic a-amino acids such as allenylglycines 3 are attractive candidates for the specific inhibition of vitamin B6-linked (pyridoxal-linked) enzyme systems; [3] a-allenyl DOPA, for example, rapidly inactivates porcine kidney aromatic amino acid decarboxylase. [4] R3 NH2 These kinds of unsaturated amino acids are challenging target molecules in asymmetric synthesis because of their known tendency towards racemization and their tautomerization to unstable a,~-dehydro amino acidsP] Together with a few methods for the synthesis of racemic a-alkynylglycines [6,7] and a-allenylphenylalanines, [8] efficient methods for the asymmetric construction of vinyIJ9-12] and alkynylglycines [13][14][15] have already been developed, but asymmetric syntheses for allenyl amino acids are still lacking. While studying asymmetric syntheses of nonproteinogenic a-amino acids, we took special interest in a-allenyl amino acids 3, because these amino acids have been recognized as irreversible enzyme inhibitors.…”