A high yielding synthesis of the acyclic precursor of the penicillins, δ— (L—α—aminoadipyl)—L—cysteinyl—D— valine (LLD-ACV) was developed. Using this synthesis the isotopically enriched ACV peptides,
δ-(DL-α—aminoadipyl)—L—cysteinyl—D— (3R)— [4-¹ ³C]—valine and δ—(L—α -
aminoadipyl)—L— [3-¹ ³c]—cysteinyl-D— [¹ ³N]—valine were prepared. In
an extension to this work the tetrapeptide, δ— (L—α—aminoadipyl)— L—
cysteinyl—D— valylglycine (LLD-ACVG) was prepared.A putative intermediate in the biosynthesis of isopenicillin N,
N— [δ— (L—α—aminoadipyl)—L—cysteinyl ]—N—hydroxy—D—valine (LLD-AC( N-OH) V),
was synthesised from N—hydroxy—D—valine benzyl ester.A cell-free system capable of converting δ— (L—α—aminoadipyl )—L—
cysteinyl—D—valine to isopenicillin N was obtained from cultures of
the cephalosporin producing fungus Cephalosporium acremonium CW19.
The cell-free system was used to test the importance of the above
synthesised compounds in penicillin biosynthesis. N— [ δ— (L—α—aminoadipyl )—L—cysteinyl ]-N—hydroxy—D—valine was shown not to be a substrate for the enzyme "isopenicillin N synthetase" but to be a
potent inhibitor of the LLD-ACV to isopenicillin N conversion. The
tetrapeptide, δ— (L—α—aminoadipyl )—L—cysteinyl—D—valylglycine, was
found to be a weak inhibitor of this conversion.The isotopically enriched ACV peptides were used to confirm the
stereochemistry of the valine C3 centre in biosynthesised δ— (L—α—
aminoadipyl)—L—cysteinyl—D—valine and to allow preliminary ¹ ³C n.m.r.
studies on the biosynthesis of isopenicillin N
