Enantiomerically Pure α-Amino Acid Synthesis via Hydroboration−Suzuki Cross-Coupling

Abstract

The Garner aldehyde-derived methylene alkene 5 and the corresponding benzyloxycarbonyl compound 25 undergo hydroboration with 9-BBN-H followed by palladium-catalyzed Suzuki coupling reactions with aryl and vinyl halides. After one-pot hydrolysis-oxidation, a range of known and novel nonproteinogenic amino acids were isolated as their N-protected derivatives. These novel organoborane homoalanine anion equivalents are generated and transformed under mild conditions and with wide functional group tolerance: electron-rich and -poor aromatic iodides and bromides (and a vinyl bromide) all undergo efficient Suzuki coupling. The extension of this methodology to prepare meso-DAP, R,R-DAP, and R,R-DAS is also described.

Synthesis and solution conformation studies of 3-substituted uridine and pseudouridine derivatives

“…The resulting alcohol 24 was oxidized to the corresponding carboxylate 25 in high yield using pyridinium dichromate (PDC). 28 The protective groups were removed under acidic conditions (TFA/H 2 O) to give the desired product 26 in good yield (71% from compounds 17 and 22).…”

Synthesis of Unnatural/Nonproteinogenic α‐Amino Acids

“…The Suzuki reaction has proven useful for the latter, although the amino acid does need to be protected (Scheme 12.11) [41], and sometimes the protected amino alcohol, rather than acid, has been employed [42][43][44].…”

Metal‐Catalyzed Cross‐Coupling Reactions of Organoboron Compounds with Organic Halides

“…The B-alkyl coupling reaction proceeds readily on the polymer surface, as has been demonstrated in the preparation of members of several structurally distinct prostaglandin (PG) classes (193) [275]. A hydroboration-cross-coupling strategy has been extensively studied in the synthesis of biologically active compounds, including: a novel class of glycomimetic compounds, aza-C-disaccharides [276]; sphingofungin F (which acts as a serinepalmitoyl transferase inhibitor) [262]; aloperine, a member of a rare family of C 15 Lupine alkaloids [277]; 5-alkylresorcinols with DNA-cleaving properties [258]; a fungal metabolite, caloporoside [265]; (þ)-aspicilin [278], an inhibitor of VCAN-1; (þ)-halichlorine [279], a cytotoxic polyketide marine natural product, callystatin A [280]; a macrolide antibiotic, 5,6-dihydrocineromycin B [281]; natural and unnatural pinnanic acids which mediate anti-inflammatory properties [282]; a chemically and metabolically stable prostaglandin analogue, carbacyclin [283]; and enantiomerically pure a-amino acids [254,256,274,284,285].…”