Methods and compositions

A method of producing a polypeptide comprising 2,3-diamino propionic acid (DAP), said method comprising genetically incorporating an unnatural amino acid into a polypeptide, wherein the unnatural amino acid is of formula (I) or (II):

• or salts, solvates, tautomers, isomers, or mixtures thereof;
• wherein:
• R1 is H, an amino acid residue, or a peptide;
• R2 is H, C1-6 alkyl, C1-6 haloalkyl, or C5-20 aryl;
• q is 1, 2, or 3;
• each R3 or R4 is independently selected from H, halo, C1-6 alkyl, C1-6 haloalkyl, C5-20 aryl, C3-20 heteroaryl, OC1-6 alkyl, SC1-6 alkyl, NH(C1-6 alkyl), and N(C1-6 alkyl)2;
• X is X1—Y, S—S—R5, Se—Se—R5, O—NH—R5, S—NH—R5, Se—NH—R5, X2—Y1, X3—Y2, N3, or NH—S(O)2—Y3;
• X1 is S, Se, O, NH, or N(C1-6 alkyl);
• X2 is S, Se, or O;
• X3 is NH—C(O)—O;
• X4 is NH—C(O)—O, O, S, or NH;
• R5 is selected from H, halo, C1-6 alkyl, C1-6 haloalkyl, C5-20 aryl, C3-20 heteroaryl, OC1-6 alkyl, NH(C1-6 alkyl), N(C1-6 alkyl)2, peptides, sugars, C3-20 heterocyclyl, and nucleic acids;
• Y is a protecting group selected from:
• R6 is selected from H, C1-6 alkyl, C1-6 haloalkyl, CO2H, CO2R′, SO2H, SO2R′, C5-20 aryl, C3-20 heteroaryl, NHC(O)R′, and NHR′;
• R7 and R8 are independently selected from H, OH, O(C1-6 alkyl), O(C5-20 aryl), and O(C3-20 heteroaryl);
• or R7 and R8 are linked together to form an O—CH2—O group;
• each R′ is independently selected from C1-6 alkyl, C1-6 haloalkyl, and C5-20 aryl;
• R9 is selected from H, C1-6 alkyl, C1-6 haloalkyl, CO2H, CO2R′, SO2H, SO2R′, and C5-20 aryl;
• R10 is selected from H, C1-6 alkyl, and C1-6 haloalkyl;
• R11 is selected from H, C1-6 alkyl, and C1-6 haloalkyl;
• X5 is S, O, NH, N—C(O)—O—R′, N—S(O)2H, N—S(O)2R′, or NR′;
• Y1 is a protecting group selected from:
• Y2 is a protecting group selected from:
• t-Bu, and CH2Ph;
• M+ is Li+, Na+, K+, or N(R13)4+;
• Z is Si or Ge;
• R12 is C1-6 alkyl or C(O)—(C5-20 aryl);
• R13 is H, C1-6 alkyl, allyl, or C5-20 aryl;
• and
• Y3 is a protecting group
• wherein the method comprises:
• (i) providing a nucleic acid encoding the polypeptide, wherein said nucleic acid comprises an orthogonal codon encoding the unnatural amino acid;
• and
• (ii) translating said nucleic acid in the presence of an orthogonal tRNA synthetase/tRNA pair capable of recognising said orthogonal codon and incorporating said unnatural amino acid into the polypeptide chain,
• wherein said orthogonal codon comprises an amber codon (TAG), said tRNA comprises Methanosarcina barkeri tRNACUA (MbtRNACUA), and said tRNA synthetase comprises the Methanosarcina barkeri pyrrolysyl-tRNA synthetase (MbPylRS synthetase) of SEQ ID NO:
• 3.