Erythro-AHPA

Figure 18. Structures of HIV protease inhibitor KNI-272 and its component (2S,3S)-3-amino-2-hydroxy-4-phenylbutanoic acid (erythro-AHPA., 66).

It seems that the syn selectivity in the nitroaldol reaction can best be explained as arising from steric hindrance in the bicyclic transition state it seems that the greater stereoselectivity obtained by use of catalysts 27 and 28 can be ascribed to increased catalyst stability, even in the presence of an excess of highly acidic nitroalkanes. The syn-selective asymmetric nitroaldol reaction was successfully applied to the catalytic asymmetric synthesis of t/zreo-dihydrosphingosine 45, which elicits a variety of cellular responses by inhibiting protein kinase C. An efficient synthesis of erythro-AHPA 42 from L-phenylalanine was, moreover, achieved by using LLB (Sch. 9) [59],... 

Schemes. Diastereoselective nitroaldol reaction as key step in the synthesis of erythro-AHPA 34...

The diastereoselective catalytic asymmetric nitroaldol reaction for the preparation of erythro-AHPA, a subunit of the promising HIV-protease inhibitors KNI-227 and KNI-272, has also been developed for industrial-scale application and will be carried out by Kaneka Co. upon request (86,87). 

---