Reaction SMILES: O=[CH:2][CH2:3][CH2:4][CH:5]1[N:9]([C:10]([O:12][CH2:13][C:14]2[CH:19]=[CH:18][C:17]([O:20][C@H:21]3[C@H:26]([O:27][C:28](=[O:30])[CH3:29])[C@@H:25]([O:31][C:32](=[O:34])[CH3:33])[C@H:24]([O:35][C:36](=[O:38])[CH3:37])[C@@H:23]([C:39]([O:41][CH3:42])=[O:40])[O:22]3)=[C:16]([NH:43][C:44](=[O:65])[CH2:45][CH2:46][NH:47][C:48]([O:50][CH2:51][CH:52]3[C:64]4[CH:63]=[CH:62][CH:61]=[CH:60][C:59]=4[C:58]4[C:53]3=[CH:54][CH:55]=[CH:56][CH:57]=4)=[O:49])[CH:15]=2)=[O:11])[CH2:8][CH2:7][O:6]1.C(#N)C.[CH3:69][C@@H:70]1[O:75][C@@H:74]([O:76][C@@H:77]2[C:82]3=[C:83]([OH:100])[C:84]4[C:96](=[O:97])[C:95]5[C:90](=[CH:91][CH:92]=[CH:93][C:94]=5[O:98][CH3:99])[C:88](=[O:89])[C:85]=4[C:86]([OH:87])=[C:81]3[CH2:80][C@@:79]([OH:105])([C:101]([CH2:103][OH:104])=[O:102])[CH2:78]2)[CH2:73][C@H:72]([NH2:106])[C@@H:71]1[OH:107].Cl.C([BH3-])#N.[Na+]>O>[OH:107][CH:71]1[CH:72]([NH:106][CH2:2][CH2:3][CH2:4][CH:5]2[N:9]([C:10]([O:12][CH2:13][C:14]3[CH:19]=[CH:18][C:17]([O:20][C@H:21]4[C@H:26]([O:27][C:28](=[O:30])[CH3:29])[C@@H:25]([O:31][C:32](=[O:34])[CH3:33])[C@H:24]([O:35][C:36](=[O:38])[CH3:37])[C@@H:23]([C:39]([O:41][CH3:42])=[O:40])[O:22]4)=[C:16]([NH:43][C:44](=[O:65])[CH2:45][CH2:46][NH:47][C:48]([O:50][CH2:51][CH:52]4[C:53]5[CH:54]=[CH:55][CH:56]=[CH:57][C:58]=5[C:59]5[C:64]4=[CH:63][CH:62]=[CH:61][CH:60]=5)=[O:49])[CH:15]=3)=[O:11])[CH2:8][CH2:7][O:6]2)[CH2:73][CH:74]([O:76][CH:77]2[C:82]3[C:81](=[C:86]([OH:87])[C:85]4[C:88](=[O:89])[C:90]5[C:95]([C:96](=[O:97])[C:84]=4[C:83]=3[OH:100])=[C:94]([O:98][CH3:99])[CH:93]=[CH:92][CH:91]=5)[CH2:80][C@@:79]([OH:105])([C:101](=[O:102])[CH2:103][OH:104])[CH2:78]2)[O:75][CH:70]1[CH3:69]
Reactant: COc1cccc2c1C(=O)c1c(O)c3c(c(O)c1C2=O)C[C@@](O)(C(=O)CO)C[C@@H]3O[C@H]1C[C@H](N)[C@H](O)[C@H](C)O1
Reactant: COC(=O)[C@H]1O[C@@H](Oc2ccc(COC(=O)N3CCOC3CCC=O)cc2NC(=O)CCNC(=O)OCC2c3ccccc3-c3ccccc32)[C@H](OC(C)=O)[C@@H](OC(C)=O)[C@@H]1OC(C)=O
Agent: Cl
Agent: [BH3-]C#N
Agent: [Na+]
Solvent: CC#N
Solvent: O
Product: COC(=O)[C@H]1O[C@@H](Oc2ccc(COC(=O)N3CCOC3CCCNC3CC(OC4C[C@](O)(C(=O)CO)Cc5c(O)c6c(c(O)c54)C(=O)c4c(OC)cccc4C6=O)OC(C)C3O)cc2NC(=O)CCNC(=O)OCC2c3ccccc3-c3ccccc32)[C@H](OC(C)=O)[C@@H](OC(C)=O)[C@@H]1OC(C)=O
Yield: 41 %

Procedure:
To the aldehyde 14 (36 mg, 0.04 mmol) in a mix of acetonitrile and water (2:1; 4.5 mL total) at 0° C. was added doxorubicin-HCl (15) followed by stirring until all the solids were dissolved. The mixture was treated with a solution of sodium cyanoborohydride (1.0M solution in THF; 20 μL, 0.02 mmol)). The reaction mixture was stirred for 2 h and the mixture was poured into water and extracted repeatedly with dichloromethane (5×50 mL). The combined organics were washed with water and brine and were concentrated under reduced pressure. The resulting residue was dissolved in 5% methanol in dichloromethane and was aspirated directly onto a 1 mm radial Chromatotron plate and eluted with 20% methanol in dichloromethane. The first major band was collected to give 23.6 mg (41%) of 16: 1H NMR (d6-DMSO); δ1.14 (d, 3H, J=6.5 Hz), 1.36-1.60 (b, 2H), 1.62-1.78 (b, 2H), 1.97-1.99 (m, 9H), 2.14 (b, 3H), 2.95 (s, 3H), 3.18-3.32 (m, 2H), 3.52 (b, 1H), 3.60 (s, 3H), 3.75 (q, 1H, J=6.8 Hz), 4.95 (bs, 1H), 3.96 (s, 3H), 4.09 (b, 1H), 4.17 (t, 1H, J=6.5 Hz), 4.25 (d, 2H, J=6.1 Hz), 4.54 (d, 2H, J=6.3 Hz), 4.70 (d, 1H, J=10.0 Hz), 4.86 (t, 1H, J=5.9 hz), 4.92-5.07 (m, 3H), 5.15 (t, 1H, J=8.2 Hz), 5.25 (bs, 1H), 5.04 (d, 1H, J=2.0 Hz), 5.48 (t, 1H, J=10.0 Hz), 5.55 (d, 1H, J=8.0 Hz), 7.0-7.11 (m, 2H), 7.28 (m, 2H), 7.37 (t, 3H, J=7.3 Hz), 7.65 (d, 3H, J=7.0 Hz), 7.85 (d, 2H, J=7.6 Hz), 8.75 (b, 1H); LC-MS m/z (ES−), 1428.9 (M−H)−, 7.9 min.