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Chiral or achiral (Z)-crotylorganoboron compounds add preferentially anti to N-(tert-butoxycarbonyl)amino aldehydes. N-(tert-Butoxycarbonyl)prolinal 3 presents a remarkably high diastereofacial selectivity. Double stereodifferentiation, starting from compound 3, allows complete diastereoselective access to the γ-amino-β-hydroxy-α-methyl acid dolaproine 1 present in the antiproliferative dolastatin 10.

A stepwise synthesis of dolastatin 10 starting from the dolaphenine residue is described. The chiral dola isoleuine and dolaproine residues were obtained by 5-step procedures from the corresponding N-Boc amino acid. The key steps are respectively the NaBH4 reduction of an allylic ketone and the addition of an achiral Z-crotylboronate on the N-Boc-L-prolinal. Peptidic couplings were efficiently realised with reagents developed in the laboratory.