Jun.22,2006  5  US 2006/0135784 Al  used, and especially, sulfonyl halide compounds (i.e. leaving  group Lis a sulfonyloxy group) are preferably used. Most  preferable combination of S 2  and leaving group L is that  wherein S 2  is an ester residue and leaving group L is a  sulfonyloxy group.  [0051]  The N-protected-3-aminopropionic acid deriva› tives (3) synthesized as described above may be isolated  and/or purified by a conventional method such as extraction,  crystallization, distillation, chromatography or the like.  However, from the operational and/or economical viewpoint  in the industrial production, the products may be used in the  next reaction as they are without isolation and/or purification  by the above conventional method.  [0052]  Next described is the second step wherein a steric  configuration at 2-position carbon of N-protected-3-amino- droxypropionic acid derivatives ( 4)] to enantiomer excess  (% e.e.) or diastereomer excess(% d.e.) of a starting material  [in this case, N-protected-3-aninopropionic acid derivatives  (3)].  [0055]  In this step, oxazolidinone derivatives are usually  obtained as the substituted-3-amino-2-hydroxypropionic  acid derivatives ( 4) having an inverted steric configuration at  2-position carbon. However, as described below in more  detail, for example, if water coexists at the beginning of this  step for the purpose of producing 3-amino-2-hydroxypropi› onic acid derivatives in a high quality and a high yield, plural  compounds can be formed as the substituted-3-amino-2- hydroxypropionic acid derivatives (4) having an inverted  steric configuration at 2-position carbon. The typical  examples are shown in the following scheme:  propionic acid derivatives (3) is inverted to convert the  derivatives  into  substituted-3-amino-2-hydroxypropionic  acid derivatives (4).  [0053]  In this step, the N-protected-3-aminopropionic acid  derivatives (3) obtained in the first step can be converted into  substituted-3-amino-2-hydroxypropionic acid derivatives  ( 4) having an inverted steric configuration at 2-position  carbon, in a high steric inversion ratio. In this case, the  N-protected-3-aminopropionic acid derivatives (3) synthe› sized in the above first step may be occasionally converted  into substituted-3-amino-2-hydroxypropionic acid deriva› tives ( 4) having an inverted steric configuration at 2-position  carbon under reaction conditions of the above first step.  However, the process is included within the production  process according to the present invention so far as the  above N-protected-3-aminopropionic acid derivatives (3)  are once formed as an intermediate.  [0054]  In this step, the inversion of a steric configuration  at 2-position carbon can proceed with an essentially perfect  inversion. The steric inversion ratio at 2-position carbon in  the products can be expected to be at least 95% or more,  usually 98% or more, preferably 100%. In this connection,  the steric inversion ratio means, as a general concept, a ratio  of enantiomer excess (% e.e.) or diastereomer excess (%  d.e.) of a product having an inverted steric configuration at  2-position carbon [in this case, substituted-3-amino-2-hy- [0059]  The formation mechanism of these inversion prod› ucts is presumed as follows.  [0060]  Firstly, oxazolinium derivative (4a) is formed by  substitution of leaving group L ofN-protected-3-aminopro› pionic acid derivative (3) through a nucleophilic substitution  reaction by carbonyl oxygen of an alkoxycarbonyl group  (-COOR 4 )  in the same molecule. The leaving group L  eliminated in this substitution reaction can form a salt with  oxazolinium derivative ( 4a) as a counter anion.  If R 3  is a  hydrogen atom, of course, the structure of the oxazolinium  derivative (4a) maybe represented as oxazoline derivative  ( 4d) formed by deprotonation.  [0061]  N-alkoxycarbonyl-3-amino-2-hydroxypropionic  acid derivative ( 4b) can be formed by hydrolysis of the  above oxazolinium derivative (4a), or by direct substitution  of leaving group L of N-protected-3-aminopropionic acid  derivative (3) with water.  [0062]  The oxazolidinone derivative (4c) can be formed  by hydrolysis or the like of the above oxazolinium derivative  [0056]  wherein R1, R 2 , R 3 , R 4  and S 3  are as defined  above;  [0057]  L represents a leaving group; and  [0058]  S 7 , S 8  and S 9  represent a hydrogen atom or an  ester residue.  R3  R3  (R 3 ~H)  I  I  R $^{1}$R$^{2}$C-N-COOR4  R $^{1}$R$^{2}$C-N  R $^{1}$R$^{2}$C-N  I '~C-OR 4  I  ~C-OR 4  I  L-CH  ----- He-cf"’  HC-0/  I  coos 3  I  coos 7  I  coos 7  (3)  /  (4a)  (4d)  !  !  R3  R3  R3  I  I  I  R $^{1}$R$^{2}$C-N-COOR4  R $^{1}$R$^{2}$C-N  R $^{1}$R$^{2}$C-N-H  I  ’--c-oR 4  I  HC-O-H  I  COOS 8  (4b)  ----- ----- I  HC-0/  HC-OH  I  I  coos 9  COOR  (4c)  (1) 