37783-51-0 Cyclic(glycyl-L-prolylglycyl-L-prolylglycyl-L-prolyl) Cyclo(pro-gly)3 Cyclo(tri(pro-gly)) Cyclo(tri(prolylglycyl)) Cyclo-(L-prolyglycyl)(3) Cyclo-(L-prolyl-glycyl)(3) c(PG)3