10.1016/S0040-4039(00)87909-5
The study in the literature presents a new one-pot synthesis method for 3-amino-β-lactams, which are valuable intermediates for producing various β-lactam antibiotics, including penicillins and cephalosporins. The key chemicals involved are zinc enolates derived from N-protected amino acid esters and imines. Specifically, the zinc enolates are prepared in situ from the corresponding lithium enolates via transmetallation with zinc dichloride. These enolates then react with imines to form the desired 3-amino-β-lactams. The study highlights the high yields and trans-stereoselectivity of this synthetic route, which contrasts with reactions involving lithium enolates. The authors also note that the enolates derived from 2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentane-1-acetic acid ethyl ester (STABASE) are more stable and yield better results than those from N,N-bis(trimethylsilyl)glycine ethyl ester. The study provides detailed procedures and characterizations of the synthesized compounds, and it suggests that the trans-stereoselectivity arises from a rigid cyclic chair-like transition state of the enolate with an E-imine.
10.1016/S0040-4039(00)84713-9
The study investigates the synthesis and antibacterial activity of various derivatives of penicillin. The researchers aimed to create 6a-carboxy and 6a-carbamoyl penicillins, which are structural analogues of previously studied 6a-(hydroxymethyl) and 6a-formyl penicillins known for their stability to β-lactamases and antibacterial activity. Key chemicals involved include 6a-(hydroxymethyl)penicillanate and 6a-formyl penicillin, which served as starting materials. The researchers used reagents such as t-butyl alcohol, chromium trioxide, pyridine, acetic anhydride, and allyl alcohol to oxidize and esterify these compounds, ultimately synthesizing various penicillin carboxylates. They also attempted to prepare a 6a-carbamoyl penicillin using mixed anhydride formation and ammonia. Despite successful synthesis of several derivatives, including the allyl ester and pivaloyloxymethyl ester, the final penicillin products exhibited poor antibacterial activity.
