I claim:
1. Peptide derivatives having the general formula:
R
1 -A
1 -A
2 -A
3 -A
4 -R
2 or its salt
wherein
R
1 =H or a protective group
A
1 =H, Ile, Leu or Val
A
2 =Glu, Asp, Ser, or Thr
A
3 =Gly or Glyc
A
4 =Arg or Lys
R
2 =is a group that upon enzymatic hydrolysis gives para-nitroaniline (pNA),
with the proviso that A
3 is Gly when A
4 is Lys and Glyc when A
4 is Arg.
2. Peptide derivatives according to claim 1 wherein A
1 =Ile.
3. Peptide derivatives according to claim 1 having the formula selected from the group consisting of:
α-Ac-Ile-Glu-Gly-Lys-pNA,
α-Ac-Ile-Ser-Gly-Lys-pNA,
α-Ac-Ile-Thr-Gly-Lys-pNA, and
α-Ac-Ile-Glu-Glyc-Arg-pNA.
4. A method for quantitatively determining bacterial endotoxins in a sample which comprises incubating the sample with a Limulus clotting enzyme and a substrate for said enzyme, wherein said substrate is a peptide derivative having the following formula:
R
1 -A
1 -A
2 -A
3 -A
4 -R
2 or its salt
where
R
1 =H or a protective group
R
1 =H, Ile, Leu or Val
A
2 =Glu, Asp, Ser, or Thr
A
3 =Gly or Glyc
A
4 =Arg or Lys
R
2 =an aromatic or heterocyclic group which by enzymatic hydrolysis gives a compound R
2 -NH
2 which can be determined quantitatively,
with the proviso that A
3 is Gly when A
4 is Lys and Glyc when A
4 is Arg.
5. The method of claim 4 when A is Ile.
6. The method of claim 5 wherein said peptide derivative is selected from the group consisting of:
α-Ac-Ile-Glu-Gly-Lys-pNA,
α-Ac-Ile-Ser-Gly-Lys-pNA,
α-Ac-Ile-Thr-Gly-Lys-pNA, and
α-Ac-Ile-Glu-Glyc-Arg-pNA.
7. The method of claim 4 wherein said clotting enzyme is Limulus Amebocyte Lysate.
8. The method of claim 4 wherein R
2 -NH
2 is para-nitroaniline.
