| For S.7a | 0.70 g O-tetrabutyltrimethylsilyl-(L)-serine methyl ester hydrochloride S.6a |
| For S.7b | 0.70 g O-tetrabutyltrimethylsilyl-(D)-serine methyl ester hydrochloride S.6b |
| For S.7c | 0.77 g O-tetrabutyltrimethylsilyl-(L)-serine isopropyl ester hydrochloride S.6c |