Positively charged non-natural amino acids, methods of making thereof, and use thereof in peptides

A non-natural amino acid compound of the formula III:

• wherein
• n is an integer of from 2 to 4;
• X—Y is (CH2)z, wherein z is an integer of from 2 to 4;
• R6, R7 and R8 are, independently, hydrogen or lower branched or straight chain alkyl, alkenyl or alkynyl of C1-C5, wherein R6 is not hydrogen;
• and
• Cβ is a carbon atom and the stereochemistry at Cβ is either R or S;
• or the ester or salt thereof.

A method for screening a peptide for an activity, comprising the steps of:

• a) measuring an activity of a peptide having a selected amino acid sequence and comprising a natural amino acid;
• b) measuring the same activity of a peptide having the same amino acid sequence but substituted independently in place of at least one natural amino acid, is a non-natural amino acid having the formula I or III:
• wherein
• n is an integer of from 2 to 4;
• R1, R2, R3 and R13 are, independently, hydrogen or lower branched or straight chain alkyl, alkenyl or alkynyl of C1-C5;
• and
• Cα and Cβ are carbon atoms and the stereochemistry at Cα and Cβ is, independently, either R or S;
• or the ester or salt thereof wherein
• when R1, R2, R3 and R13 are all hydrogen, then n is not 2 or 3,
• when n is 2 or 3, R1 and R13 are hydrogen, and R2 and R3 are independently hydrogen or methyl with at least one of R2 and R3 being methyl, then the stereochemistry at Cβ is not S, and
• when n is 4, and R1, R2, R3 and R13 are all hydrogen, then the stereochemistry at Cβ is not R;
• or
• wherein
• n is an integer of from 2 to 4;
• X—Y is (CH2)z, wherein z is an integer of from 2 to 4;
• R6, R7 and R8 are, independently, hydrogen or lower branched or straight chain alkyl, alkenyl or alkynyl of C1-C5;
• and
• Cβ is a carbon atom and the stereochemistry at Cβ is either R or S;
• or the ester or salt thereof.

A method of treating or preventing in a subject a disease treated or prevented by the administration of a peptide, comprising administering to the subject a peptide having, substituted for a natural amino acid, at least one non-natural amino acid having the following formula I or III:

• wherein
• n is an integer of from 2 to 4;
• R1, R2, R3 and R13 are, independently, hydrogen or lower branched or straight chain alkyl, alkenyl or alkynyl of C1-C5;
• and
• Cα and Cβ are carbon atoms and the stereochemistry at Cα and Cβ is, independently, either R or S;
• or the ester or salt thereof, wherein
• when R1, R2, R3 and R13 are all hydrogen, then n is not 2 or 3,
• when n is 2 or 3, R1 and R13 are hydrogen, and R2 and R3 are independently hydrogen or methyl with at least one of R2 and R3 being methyl, then the stereochemistry at Cβ is not S, and
• when n is 4, and R1, R2, R3 and R13 are all hydrogen, then the stereochemistry at Cβ is not R;
• or
• wherein
• n is an integer of from 2 to 4;
• X—Y is (CH2)z, wherein z is an integer of from 2 to 4;
• R6, R7 and R8 are, independently, hydrogen or lower branched or straight chain alkyl, alkenyl or alkynyl of C1-C5, wherein R6 is not hydrogen;
• and
• Cβ is a carbon atom and the stereochemistry at Cβ is either R or S;
• or the ester or salt thereof.

A method of treating or preventing in a subject a disease treated or prevented by the administration of a peptide, comprising administering to the subject a peptide having, substituted for a natural amino acid, at least one non-natural amino acid having the following formula III:

• wherein
• n is an integer of from 2 to 4;
• X—Y is (CH2)z, wherein z is an integer of from 2 to 4;
• R6, R7 and R8 are, independently, hydrogen or lower branched or straight chain alkyl, alkenyl or alkynyl of C1-C5;
• and
• Cβ is a carbon atom and the stereochemistry at Cβ is either R or S;
• or the ester or salt thereof,
• wherein the peptide is not luteinizing hormone and releasing hormone or an analog thereof.