, ▁the ▁car b ony l ▁carbon ▁is ▁ 2 , ▁the ▁α - car bon ▁is ▁ 3 , ▁and ▁the ▁ β - car bon ▁ 4 . ▁ ▁B ios yn thesis ▁To ▁date , ▁two ▁distinct ▁methods ▁of ▁b ios yn thes izing ▁the ▁ β - la ct am ▁core ▁of ▁this ▁family ▁of ▁ant ib iot ics ▁have ▁been ▁discovered . ▁The ▁first ▁path way ▁discovered ▁was ▁that ▁of ▁the ▁pen ams ▁and ▁ce ph ems . ▁This ▁path ▁begins ▁with ▁a ▁ ▁non rib os om al ▁pe pt ide ▁synth et ase ▁( NR PS ), ▁AC V ▁synth et ase ▁( AC VS ), ▁which ▁generates ▁the ▁linear ▁tri pe pt ide ▁ δ -( L - α - am ino ad ip yl )- L - c yst e ine - D - val ine ▁( AC V ). ▁AC V ▁is ▁ox id atively ▁cycl ized ▁( two ▁cycl izations ▁by ▁a ▁single ▁en zym e ) ▁to ▁b icy clic ▁intermediate ▁is open ic ill in ▁N ▁by ▁is open ic ill in ▁N ▁synth ase ▁( IP NS ) ▁to ▁form ▁the ▁pen am ▁core ▁structure . ▁Vari ous ▁trans am id ations ▁lead ▁to ▁the ▁different ▁natural ▁pen ic ill ins . ▁ ▁The ▁b ios yn thesis ▁of ▁ce ph ems ▁branch ▁off ▁at ▁is open ic ill in ▁N ▁by ▁an ▁ox id ative ▁ring ▁expansion ▁to ▁the ▁ce ph em ▁core . ▁As ▁with ▁the ▁pen