In layer structure 20 of a semiconductor laser of a surface emitting type, 21 and 24 represent an n-type contact layer made of n-type GaN and a p-layer made of p-type AlGaN, respectively. In a first mode, the batter is preferably handled by mixing up one batch at a time from materials whose input quantities are specified in terms of defined weight-ratios, and then the batch is used up completely until depleted. The system additionally includes an airflow control assembly operably coupled to the second end of the outer tube, and an inner tube, concentric to the outer tube, having a first end and a second end, the first end operably coupled to the airflow control assembly, the second end in communication with the primary chamber of the vacuum booster assembly. The cover is adjustable between said positions by means of an adjusting mechanism comprising two substantially parallel guides arranged in the longitudinal direction of the housing, for adjusting the cover along the guides. The washer stack includes a wear washer having an annular generally external ledge for forming a generally L-shape cross section rotatable with the spindle in an annular generally stationary washer adjacent to the swivel and riding on the wear washer external ledge without touching the spindle so that spindle wear is reduced by the wear washer rotating relative to the generally stationary washer. Sitagliptin is synthesized by using chiral amino compounds as a raw material, without having to build a chiral center with a chiral asymmetric catalytic hydrogenation, and high-pressure hydrogenation is avoided.