First reduction in pentose phosphate pathway is

The first reduction in the pentose phosphate pathway is the Oxidation of glucose 6-phosphate.
The pentose phosphate pathway (PPP) branches from glucose 6-phosphate (G6P), produces NADPH and ribose 5-phosphate and shunts carbons back to the glycolytic or gluconeogenic pathway.
The first enzyme in this pathway is glucose-6-phosphate dehydrogenase (G6PDH) which produces NADPH, a substrate utilized for lipogenesis and glutathione regeneration by glutathione reductase.
The PPP has been demonstrated to be a major regulator for cellular reduction-oxidation (redox) homeostasis and biosynthesis.