Nanoluc suicide substrates

A compound of formula (I)

• or a tautomer or a salt thereof, wherein:
• R1 is optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocycle, or optionally substituted cycloalkyl, wherein R1 is substituted with at least one group that is -Q-L-Z;
• Q is —O—, —NRQ—, —NRQ—CO—, —CO—NRQ—, —O—CO—NRQ—, or —NRQ—CO—O—;
• L is —(CR1aR1b)m—, —(CR1xR1y—CR1xR1y—O)t1—(CR1xR1y)t2-Q1-, —(CR1xR1y)t2-A-(CR1xR1y—CR1xR1y—O)t1-Q1-, —(CR1xR1y)t3-A-(CR1xR1y—CR1xR1y—O)t1—(CR1xR1y)t2—, or —(CR1xR1y)t3-A-(CR1xR1y)t4—, wherein each Q1 is independently a bond, —O—, or —NRQ1—, and each A is independently a bond, —O—, —NRQ, —NRQ—CO—, —CO—NRQ—, —O—CO—NRQ—, or —NRQ—CO—O—;
• Z is —COOR2, —SO2—OR3, —PO(OR4)(OR5), halo, azide, C2-C10 alkynyl, a biotin moiety, —NR6R7, —NR8—CO—R9, —CO—R10, or —NR11—CO—O—R12;
• R2, R3, R4, R5, R8, R9, R10, R11, and R12 at each occurrence are independently hydrogen, optionally substituted C1-C8 alkyl, optionally substituted aryl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted heteroaryl, optionally substituted heterocycle, optionally substituted heteroalkyl, or an energy acceptor;
• R6 and R7 at each occurrence are independently hydrogen, optionally substituted C1-C8 alkyl, optionally substituted aryl, optionally substituted cycloalkyl, optionally substituted heteroaryl, optionally substituted heterocycle, optionally substituted heteroalkyl, or an energy acceptor;
• or R6 and R7, together with the nitrogen atom to which they are attached, together form an optionally substituted ring;
• R1a, R1b, RQ, RQ1, R1x, and R1y at each occurrence are independently hydrogen, C1-C4 alkyl, or C1-C4 haloalkyl;
• q is 0, 1, or 2;
• m at each occurrence is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12;
• t1 at each occurrence is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
• t2 is an integer from 0-5;
• t3 at each occurrence is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
• and
• t4 is an integer from 0-5,
• wherein the compound is not 4-[4-[[8-benzyl-6-(4-hydroxyphenyl)-3-oxo-7H-imidazo[1,2-a]pyrazin-2-yl]methyl]phenoxy]butanoic acid.