(19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine

C116H115N33O5 — CID 164967770

About (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine

(19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine (PubChem CID 164967770) has the molecular formula C116H115N33O5 and a molecular weight of 2051.42 g/mol. Its IUPAC name is (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine.

Molecular Properties

• Compound Name: (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine
• PubChem CID: 164967770
• Molecular Formula: C116H115N33O5
• Molecular Weight: 2051.42 g/mol
• Exact Mass: 2049.98
• IUPAC Name: (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine
• SMILES: CCn1ncc2c1-c1ccc(C)cc1C(C)Oc1nc(cnc1N)-c1c(cnn1C)C2.CCn1ncc2c1-c1ccc(C)cc1[C@@H](C)Oc1cc(cnc1N)-c1c(cnn1C)C2.Cc1ccc2c(c1)C(C)Oc1cc(cnc1N)-c1c(cnn1C1CCC1)Cn1ccnc1-2.Cc1ccc2c(c1)[C@@H](C)Oc1cc(cnc1N)-c1c(C#N)ncn1Cc1ccnn1-2.Cc1ccc2c(c1)[C@H](C)Oc1cc(cnc1N)-c1c(C#N)ncn1Cc1ccnn1-2
• InChI: InChI=1S/C25H26N6O.C24H26N6O.C23H25N7O.2C22H19N7O/c1-15-6-7-20-21(10-15)16(2)32-22-11-17(12-28-24(22)26)23-18(14-30-9-8-27-25(20)30)13-29-31(23)19-4-3-5-19;1-5-30-23-17(13-28-30)9-16-12-27-29(4)22(16)18-10-21(24(25)26-11-18)31-15(3)20-8-14(2)6-7-19(20)23;1-5-30-20-15(11-27-30)9-16-10-26-29(4)21(16)19-12-25-22(24)23(28-19)31-14(3)18-8-13(2)6-7-17(18)20;2*1-13-3-4-19-17(7-13)14(2)30-20-8-15(10-25-22(20)24)21-18(9-23)26-12-28(21)11-16-5-6-27-29(16)19/h6-13,16,19H,3-5,14H2,1-2H3,(H2,26,28);6-8,10-13,15H,5,9H2,1-4H3,(H2,25,26);6-8,10-12,14H,5,9H2,1-4H3,(H2,24,25);2*3-8,10,12,14H,11H2,1-2H3,(H2,24,25)/t;15-;;2*14-/m.1.10/s1
• InChIKey: CSAYVZPDDCUFGY-UYIDGURJSA-N
• XLogP: 19.71
• TPSA: 479.37 Ų
• H-Bond Donors: 5
• H-Bond Acceptors: 38
• Rotatable Bonds: 3
• Heavy Atoms: 154
• Complexity: —

Lipinski Rule of Five

3 violations

Rule	Value
MW ≤ 500	2051.42
LogP ≤ 5	19.71
H-Bond Donors ≤ 5	5
H-Bond Acceptors ≤ 10	38

Frequently Asked Questions

What is the IUPAC name of (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine?

The IUPAC name of (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine (CID 164967770) is (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine.

What is the SMILES notation for (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine?

The canonical SMILES for (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine is CCn1ncc2c1-c1ccc(C)cc1C(C)Oc1nc(cnc1N)-c1c(cnn1C)C2.CCn1ncc2c1-c1ccc(C)cc1[C@@H](C)Oc1cc(cnc1N)-c1c(cnn1C)C2.Cc1ccc2c(c1)C(C)Oc1cc(cnc1N)-c1c(cnn1C1CCC1)Cn1ccnc1-2.Cc1ccc2c(c1)[C@@H](C)Oc1cc(cnc1N)-c1c(C#N)ncn1Cc1ccnn1-2.Cc1ccc2c(c1)[C@H](C)Oc1cc(cnc1N)-c1c(C#N)ncn1Cc1ccnn1-2.

What is the InChIKey of (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine?

The InChIKey is CSAYVZPDDCUFGY-UYIDGURJSA-N. The full InChI is InChI=1S/C25H26N6O.C24H26N6O.C23H25N7O.2C22H19N7O/c1-15-6-7-20-21(10-15)16(2)32-22-11-17(12-28-24(22)26)23-18(14-30-9-8-27-25(20)30)13-29-31(23)19-4-3-5-19;1-5-30-23-17(13-28-30)9-16-12-27-29(4)22(16)18-10-21(24(25)26-11-18)31-15(3)20-8-14(2)6-7-19(20)23;1-5-30-20-15(11-27-30)9-16-10-26-29(4)21(16)19-12-25-22(24)23(28-19)31-14(3)18-8-13(2)6-7-17(18)20;2*1-13-3-4-19-17(7-13)14(2)30-20-8-15(10-25-22(20)24)21-18(9-23)26-12-28(21)11-16-5-6-27-29(16)19/h6-13,16,19H,3-5,14H2,1-2H3,(H2,26,28);6-8,10-13,15H,5,9H2,1-4H3,(H2,25,26);6-8,10-12,14H,5,9H2,1-4H3,(H2,24,25);2*3-8,10,12,14H,11H2,1-2H3,(H2,24,25)/t;15-;;2*14-/m.1.10/s1.

What are the key properties of (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine?

(19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine has a molecular weight of 2051.42 g/mol, XLogP of 19.71, 3 rotatable bonds, 5 hydrogen bond donors, and 38 hydrogen bond acceptors.

Where does this data come from?

All data for (19R)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;(19S)-22-amino-16,19-dimethyl-20-oxa-4,6,11,12,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2,4,8,10,13(18),14,16,21,23-decaene-3-carbonitrile;3-cyclobutyl-16,19-dimethyl-20-oxa-3,4,8,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,9,11,13(18),14,16,21,23-decaen-22-amine;11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23,25-hexazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(24),2(6),4,8(12),9,13(18),14,16,21(25),22-decaen-22-amine;(19R)-11-ethyl-3,16,19-trimethyl-20-oxa-3,4,10,11,23-pentazapentacyclo[19.3.1.02,6.08,12.013,18]pentacosa-1(25),2(6),4,8(12),9,13(18),14,16,21,23-decaen-22-amine is sourced from PubChem (CID 164967770), the world's largest open chemistry database maintained by the National Library of Medicine (NIH).