Modified Nucleosides

1 . (canceled)

2 . (canceled)

3 . (canceled)

4 . (canceled)

5 . (canceled)

6 . (canceled)

7 . (canceled)

8 . (canceled)

9 . A compound comprising the structure of Formula IA or Formula IB:

or a salt of either one of these, wherein

each L is independently a —(CH 2 ) n —, wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;

each R 1 is independently selected from

wherein * denotes the point of attachment of the R 1 group to the L group;

each X is independently selected from —H, —OH, —OMe,

—O-allyl, —O-ethyl, —O-propyl, —OCH 2 CH 2 OCH 3 , -fluoro, tert-butyldimethylsilyloxy, —NH 2 , and -azido;

each R 2 is independently selected from —OH; -acetyl; —OBz;

—OP(N(CH 2 CH 3 ) 2 )(OCH 2 CH 2 CN), —OP(N(R x ) 2 )(OCH 2 CH 2 CN), wherein each R x is independently (C 1-6 )alkyl; tert-butyldimethylsilyloxy; —O-ss; —OR; —SR; —ZP(Z′)(Z″)—O—R; wherein ss is a solid support, Z, Z′, and Z″ are each independently selected from O and S, and R is an adjacent nucleotide;

each R 3 is independently selected from —OH, —O-trityl, —O-4,4′-dimethoxytrityl, —O-triphosphate, —OR, —SR, —NH 2 , —NHR, and —Z—P(Z′)(Z″)O—R, wherein Z, Z′, and Z″ are each independently selected from O and S, and R is an adjacent nucleotide.

10 . The compound of claim 9 , wherein n is 1, 2, or 3.

11 . (canceled)

12 . (canceled)

13 . The compound of claim 9 , wherein each R 1 is independently selected from

14 . (canceled)

15 . A compound comprising the structure of Formula IIA or Formula IIB:

or a salt of either one of these, wherein

each L is independently a —(CH 2 ) n —, wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;

each R 1 is independently selected from

wherein * denotes the point of attachment of the R 1 group to the L group;

each X is independently selected from —H, —OH, —OMe,

—O-allyl, —O-ethyl, —O-propyl, —OCH 2 CH 2 OCH 3 , -fluoro, tert-butyldimethylsilyloxy, —NH 2 , and -azido.

16 . The compound of claim 15 , wherein n is 1, 2, or 3.

17 . (canceled)

18 . (canceled)

19 . The compound of claim 15 , wherein each R 1 is independently selected from:

20 . A compound comprising the following structure:

or a salt of any one of these;

wherein each X is independently selected from —H, —OH,

—O-methyl, —O-allyl, —O-ethyl, —O-propyl, —OCH 2 CH 2 OCH 3 , -fluoro, tert-butyldimethylsilyloxy, —NH 2 , and -azido.

21 . (canceled)

22 . (canceled)

23 . An oligonucleotide comprising the compound of claim 9 .

24 . (canceled)

25 . (canceled)

26 . The oligonucleotide of claim 23 , which is an aptamer that binds a target.

27 . (canceled)

28 . (canceled)

29 . (canceled)

30 . (canceled)

31 . (canceled)

32 . (canceled)

33 . An aptamer comprising at least one first 5-position modified pyrimidine and at least one second 5-position modified pyrimidine, wherein the first 5-position modified pyrimidine and the second 5-position modified pyrimidine are different 5-position modified pyrimidines, and wherein the at least one first 5-position modified pyrimidine is a compound according to claim 9 .

34 . (canceled)

35 . (canceled)

36 . (canceled)

37 . A composition comprising a plurality of aptamers of claim 33 .

38 . (canceled)

39 . (canceled)

40 . A composition comprising an aptamer and a target, wherein the aptamer and the target are capable of forming a complex, and wherein the aptamer is an aptamer of claim 33 .

41 . (canceled)

42 . The composition of claim 40 , wherein the target is selected from a protein, a peptide, a carbohydrate, a small molecule, a cell, and a tissue.

43 . (canceled)

44 . A pharmaceutical composition comprising at least one aptamer of claim 33 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

45 . (canceled)

46 . A method of treating or preventing a disease or condition in a subject, comprising administering to a subject in need thereof an aptamer of claim 33 .

47 . (canceled)

48 . (canceled)

49 . A method comprising:

(a) contacting an aptamer capable of binding to a target molecule with a sample;

(b) incubating the aptamer with the sample to allow an aptamer-target complex to form;

(c) enriching for the aptamer-target complex in the sample; and

(d) detecting for the presence of the aptamer, the aptamer-target complex, or the target molecule, wherein the detection of the aptamer, the aptamer-target complex, or the target molecule indicates that the target molecule is present in the sample, and wherein the lack of detection of the aptamer, the aptamer-target complex, or the target molecule indicates that the target molecule is not present in the sample;

wherein the aptamer comprises an aptamer of claim 33 .

50 . (canceled)

51 . (canceled)

52 . (canceled)

53 . (canceled)

54 . (canceled)

55 . (canceled)

56 . A method for detecting a target in a sample comprising:

(a) contacting the sample with a first aptamer to form a mixture, wherein the first aptamer is capable of binding to the target to form a first complex;

(b) incubating the mixture under conditions that allow for the first complex to form;

(c) contacting the mixture with a second aptamer, wherein the second aptamer is capable of binding the first complex to form a second complex;

(d) incubating the mixture under conditions that allow for the second complex to form;

(e) detecting for the presence or absence of the first aptamer, the second aptamer, the target, the first complex or the second complex in the mixture, wherein the presence of the first aptamer, the second aptamer, the target, the first complex or the second complex indicates that the target is present in the sample;

wherein the first aptamer comprises a compound of claim 9 ; and

wherein the second aptamer comprises at least one second 5-position modified pyrimidine;

wherein the first aptamer, the second aptamer and the target are capable of forming a trimer complex.

57 . (canceled)

58 . (canceled)

59 . (canceled)

60 . (canceled)

61 . A method for identifying one or more aptamers capable of binding to a target molecule comprising:

(a) contacting a library of aptamers with the target molecule to form a mixture, and allowing for the formation of an aptamer-target complex, wherein the aptamer-target complex forms when an aptamer has affinity for the target molecule;

(b) partitioning the aptamer-target complex from the remainder of the mixture (or enriching for the aptamer-target complex);

(c) dissociating the aptamer-target complex; and

(d) identifying the one or more aptamers capable of binding to the target molecule;

wherein the library of aptamers comprises a plurality of polynucleotides, and which is the composition of claim 37 .

62 . (canceled)

63 . (canceled)

64 . (canceled)

65 . (canceled)

66 . (canceled)

67 . (canceled)

68 . (canceled)

69 . (canceled)

70 . (canceled)

71 . (canceled)

72 . (canceled)

73 . (canceled)

74 . (canceled)

75 . (canceled)

76 . (canceled)

77 . A kit comprising the compound of claim 9 , and optionally one or more of (a) a pharmaceutically acceptable carrier, such as a solvent or solution; (b) a pharmaceutically acceptable excipient, such as a stabilizer or buffer; (c) at least one container, vial, or apparatus for holding and/or mixing the kit components; (d) a delivery apparatus: (e) labeling agents useful to detect a target molecule that is bound to an aptamer: (f) a solid support, such as a microarray or bead; and (g) reagents related to quantitation of polymerase chain reaction products, such as intercalating fluorescent dyes or fluorescent DNA probes.

78 . (canceled)

79 . A compound comprising the structure of Formula III, Formula IV, or Formula V:

or a salt of any one of these, wherein:

each L is independently a —(CH 2 ) n —, wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;

each R 1 is independently selected from

wherein * denotes the point of attachment of the R 1 group to the L group; and

each X is independently selected from —H, —OH, —OMe,

—O-allyl, —O-ethyl, —O-propyl, —OCH 2 CH 2 OCH 3 , -fluoro, tert-butyldimethylsilyloxy, —NH 2 , and -azido.

80 . (canceled)

81 . (canceled)

82 . (canceled)

83 . (canceled)